Java Interview Questions

Question: What if the main method is declared as private?

Question: What if the static modifier is removed from the signature of the main method?

Question: What if I write static public void instead of public static void?

Q:Question: What if I do not provide the String array as the argument to the method?

Question: What is the first argument of the String array in main method?

Question: If I do not provide any arguments on the command line, then the String array of Main method will be empty of null?

Question: How can one prove that the array is not null but empty?

Question: What environment variables do I need to set on my machine in order to be able to run Java programs?

Question: Can an application have multiple classes having main method?

Question: Can I have multiple main methods in the same class?

Question: Do I need to import java.lang package any time? Why ?

Question: Can I import same package/class twice? Will the JVM load the package twice at runtime?

Question: What are Checked and UnChecked Exception?

Question: What is Overriding?

Question: What are different types of inner classes?


Q: What if the main method is declared as private?
A: The program compiles properly but at runtime it will give "Main method not public." message.




Q: What if the static modifier is removed from the signature of the main method?
A: Program compiles. But at runtime throws an error "NoSuchMethodError".




Q: What if I write static public void instead of public static void?
A: Program compiles and runs properly.




Q: What if I do not provide the String array as the argument to the method?
A: Program compiles but throws a runtime error "NoSuchMethodError".




Q: What is the first argument of the String array in main method?
A: The String array is empty. It does not have any element. This is unlike C/C++ where the first element by default is the program name.




Q: If I do not provide any arguments on the command line, then the String array of Main method will be empty of null?
A: It is empty. But not null.




Q: How can one prove that the array is not null but empty?
A: Print args.length. It will print 0. That means it is empty. But if it would have been null then it would have thrown a NullPointerException on attempting to print args.length.




Q: What environment variables do I need to set on my machine in order to be able to run Java programs?
A: CLASSPATH and PATH are the two variables.




Q: Can an application have multiple classes having main method?
A: Yes it is possible. While starting the application we mention the class name to be run. The JVM will look for the Main method only in the class whose name you have mentioned. Hence there is not conflict amongst the multiple classes having main method.




Q: Can I have multiple main methods in the same class?
A: No the program fails to compile. The compiler says that the main method is already defined in the class.




Q: Do I need to import java.lang package any time? Why ?
A: No. It is by default loaded internally by the JVM.




Q: Can I import same package/class twice? Will the JVM load the package twice at runtime?
A: One can import the same package or same class multiple times. Neither compiler nor JVM complains abt it. And the JVM will internally load the class only once no matter how many times you import the same class.




Q: What are Checked and UnChecked Exception?
A: A checked exception is some subclass of Exception (or Exception itself), excluding class RuntimeException and its subclasses.
Making an exception checked forces client programmers to deal with the possibility that the exception will be thrown. eg, IOException thrown by java.io.FileInputStream's read() method•
Unchecked exceptions are RuntimeException and any of its subclasses. Class Error and its subclasses also are unchecked. With an unchecked exception, however, the compiler doesn't force client programmers either to catch the
exception or declare it in a throws clause. In fact, client programmers may not even know that the exception could be thrown. eg, StringIndexOutOfBoundsException thrown by String's charAt() method• Checked exceptions must be caught at compile time. Runtime exceptions do not need to be. Errors often cannot be.



Q: What is Overriding?
A: When a class defines a method using the same name, return type, and arguments as a method in its superclass, the method in the class overrides the method in the superclass.
When the method is invoked for an object of the class, it is the new definition of the method that is called, and not the method definition from superclass. Methods may be overridden to be more public, not more private.



Q: What are different types of inner classes?
A: Nested -level classes, Member classes, Local classes, Anonymous classes
Nested -level classes- If you declare a class within a class and specify the static modifier, the compiler treats the class just like any other -level class.
Any class outside the declaring class accesses the nested class with the declaring class name acting similarly to a package. eg, outer.inner. -level inner classes implicitly have access only to static variables.There can also be inner interfaces. All of these are of the nested -level variety.

Member classes - Member inner classes are just like other member methods and member variables and access to the member class is restricted, just like methods and variables. This means a public member class acts similarly to a nested -level class. The primary difference between member classes and nested -level classes is that member classes have access to the specific instance of the enclosing class.

Local classes - Local classes are like local variables, specific to a block of code. Their visibility is only within the block of their declaration. In order for the class to be useful beyond the declaration block, it would need to implement a
more publicly available interface.Because local classes are not members, the modifiers public, protected, private, and static are not usable.

Anonymous classes - Anonymous inner classes extend local inner classes one level further. As anonymous classes have no name, you cannot provide a constructor.

J2ME Interview Questions

What is 3G
Third generation (3G) wireless networks will offer faster data transfer rates than current networks. The first generation of
wireless (1G) was analog cellular. The second generation (2G) is digital cellular, featuring integrated voice and data
communications. So-called 2.5G networks offer incremental speed increases. 3G networks will offer dramatically improved data
transfer rates, enabling new wireless applications such as streaming media.

What is 3GPP
The 3rd Generation Partnership Project (3GPP) is a global collaboration between 6 partners: ARIB, CWTS, ETSI, T1, TTA, and
TTC. The group aims to develop a globally accepted 3rd-generation mobile system based on GSM.

What is 802.11
802.11 is a group of specifications for wireless networks developed by the Institute of Electrical and Electronics Engineers
(IEEE). 802.11 uses the Ethernet protocol and CSMA/CA (carrier sense multiple access with collision avoidance) for path
sharing.

What is API
An Application Programming Interface (API) is a set of classes that you can use in your own application. Sometimes called
libraries or modules, APIs enable you to write an application without reinventing common pieces of code. For example, a
networking API is something your application can use to make network connections, without your ever having to understand the
underlying code.

What is AMPS
Advanced Mobile Phone Service (AMPS) is a first-generation analog, circuit-switched cellular phone network. Originally
operating in the 800 MHz band, service was later expanded to include transmissions in the 1900 MHz band, the VHF range in
which most wireless carriers operate. Because AMPS uses analog signals, it cannot transmit digital signals and cannot
transport data packets without assistance from newer technologies such as TDMA and CDMA.

What is CDC
The Connected Device Configuration (CDC) is a specification for a J2ME configuration. Conceptually, CDC deals with devices
with more memory and processing power than CLDC; it is for devices with an always-on network connection and a minimum of 2 MB
of memory available for the Java system.

What is CDMA
Code-Division Multiple Access (CDMA) is a cellular technology widely used in North America. There are currently three CDMA
standards: CDMA One, CDMA2000 and W-CDMA. CDMA technology uses UHF 800Mhz-1.9Ghz frequencies and bandwidth ranges from 115Kbs
to 2Mbps.

What is CDMA One
Also know as IS-95, CDMAOne is a 2nd generation wireless technology. Supports speeds from 14.4Kbps to 115K bps.

What is CDMA2000
Also known as IS-136, CDMA2000 is a 3rd generation wireless technology. Supports speeds ranging from 144Kbps to 2Mbps.

What is CDPD
Developed by Nortel Networks, Cellular Digital Packet Data (CDPD) is an open standard for supporting wireless Internet access
from cellular devices. CDPD also supports Multicast, which allows content providers to efficiently broadcast information to
many devices at the same time.

What is cHTML
Compact HTML (cHTML) is a subset of HTML which is designed for small devices. The major features of HTML that are excluded
from cHTML are: JPEG image, Table, Image map, Multiple character fonts and styles, Background color and image, Frame and
Style sheet.

What is CLDC
The Connected, Limited Device Configuration (CLDC) is a specification for a J2ME configuration. The CLDC is for devices with
less than 512 KB or RAM available for the Java system and an intermittent (limited) network connection. It specifies a
stripped-down Java virtual machine1 called the KVM as well as several APIs for fundamental application services. Three
packages are minimalist versions of the J2SE java.lang, java.io, and java.util packages. A fourth package,
javax.microedition.io, implements the Generic Connection Framework, a generalized API for making network connections.

What is configuration
In J2ME, a configuration defines the minimum Java runtime environment for a family of devices: the combination of a Java
virtual machine (either the standard J2SE virtual machine or a much more limited version called the CLDC VM) and a core set
of APIs. CDC and CLDC are configurations. See also profile, optional package.
What is CVM
The Compact Virtual Machine (CVM) is an optimized Java virtual machine1 (JVM) that is used by the CDC.

What is Deck
A deck is a collection of one or more WML cards that can be downloaded, to a mobile phone, as a single entity.

What is EDGE
Enhanced Data GSM Environment (EDGE) is a new, faster version of GSM. EDGE is designed to support transfer rates up to
384Kbps and enable the delivery of video and other high-bandwidth applications. EDGE is the result of a joint effort between
TDMA operators, vendors and carriers and the GSM Alliance.

What is ETSI
The European Telecommunications Standards Institute (ETSI) is a non-profit organization that establishes telecommunications
standards for Europe.

What is FDMA
Frequency-division multiple-access (FDMA) is a mechanism for sharing a radio frequency band among multiple users by dividing
it into a number of smaller bands.

What is Foundation Profile
The Foundation Profile is a J2ME profile specification that builds on CDC. It adds additional classes and interfaces to the
CDC APIs but does not go so far as to specify user interface APIs, persistent storage, or application life cycle. Other J2ME
profiles build on the CDC/Foundation combination: for example, the Personal Profile and the RMI Profile both build on the
Foundation Profile.

What is Generic Connection Framework
The Generic Connection Framework (GCF) makes it easy for wireless devices to make network connections. It is part of CLDC and
CDC and resides in the javax.microedition.io package.

What is GPRS
The General Packet Radio System (GPRS) is the next generation of GSM. It will be the basis of 3G networks in Europe and
elsewhere.

What is GSM
The Global System for Mobile Communications (GSM) is a wireless network system that is widely used in Europe, Asia, and
Australia. GSM is used at three different frequencies: GSM900 and GSM1800 are used in Europe, Asia, and Australia, while
GSM1900 is deployed in North America and other parts of the world.
What is HLR
The Home Location Register (HLR) is a database for permanent storage of subscriber data and service profiles.

What is HTTPS
Hyper Text Transfer Protocol Secure sockets (HTTPS) is a protocol for transmission of encrypted hypertext over Secure Sockets
Layer.

What is i-appli
Sometimes called "Java for i-mode", i-appli is a Java environment based on CLDC. It is used on handsets in NTT DoCoMo's
i-mode service. While i-appli is similar to MIDP, it was developed before the MIDP specification was finished and the two
APIs are incompatible.

What is IDE
An Integrated Development Environment (IDE) provides a programming environment as a single application. IDEs typically bundle
a compiler, debugger, and GUI builder tog ether. Forte for Java is Sun's Java IDE.

What is iDEN
The Integrated Dispatch Enhanced Network (iDEN) is a wireless network system developed by Motorola. Various carriers support
iDEN networks around the world: Nextel is one of the largest carriers, with networks covering North and South America.

What is i-mode
A standard used by Japanese wireless devices to access cHTML (compact HTML) Web sites and display animated GIFs and other
multimedia content.

What is J2ME
Java 2, Micro Edition is a group of specifications and technologies that pertain to Java on small devices. The J2ME moniker
covers a wide range of devices, from pagers and mobile telephones through set-top boxes and car navigation systems. The J2ME
world is divided into configurations and profiles, specifications that describe a Java environment for a specific class of
device.

What is J2ME WTK
The J2ME Wireless Toolkit is a set of tools that provides developers with an emulation environment, documentation and
examples for developing Java applications for small devices. The J2ME WTK is based on the Connected Limited Device
Configuration (CLDC) and Mobile Information Device Profile (MIDP) reference implementations, and can be tightly integrated
with Forte for Java

What is Java Card
The Java Card specification allows Java technology to run on smart cards and other small devices. The Java Card API is
compatible with formal international standards, such as, ISO7816, and industry-specific standards, such as, Europay/Master
Card/Visa (EMV).

What is JavaHQ
JavaHQ is the Java platform control center on your Palm OS device.

What is JCP
The Java Community Process (JCP) an open organization of international Java developers and licensees who develop and revise
Java technology specifications, reference implementations, and technology compatibility kits through a formal process.

What is JDBC for CDC/FP
The JDBC Optional Package for CDC/Foundation Profile (JDBCOP for CDC/FP) is an API that enables mobile Java applications to
communicate with relational database servers using a subset of J2SE's Java Database Connectivity. This optional package is a
strict subset of JDBC 3.0 that excludes some of JDBC's advanced and server-oriented features, such as pooled connections and
array types. It's meant for use with the Foundation Profile or its supersets.

What is JSR
Java Specification Request (JSR) is the actual description of proposed and final specifications for the Java platform. JSRs
are reviewed by the JCP and the public before a final release of a specification is made.

What is KittyHawk
KittyHawk is a set of APIs used by LG Telecom on its IBook and p520 devices. KittyHawk is based on CLDC. It is conceptually
similar to MIDP but the two APIs are incompatible.

What is KJava
KJava is an outdated term for J2ME. It comes from an early package of Java software for PalmOS, released at the 2000 JavaOne
show. The classes for that release were packaged in the com.sun.kjava package.

What is kSOAP
kSOAP is a SOAP API suitable for the J2ME, based on kXML.

What is kXML
The kXML project provides a small footprint XML parser that can be used with J2ME.

What is KVM
The KVM is a compact Java virtual machine (JVM) that is designed for small devices. It supports a subset of the features of
the JVM. For example, the KVM does not support floating-point operations and object finalization. The CLDC specifies use of
the KVM. According to folklore, the 'K' in KVM stands for kilobyte, signifying that the KVM runs in kilobytes of memory as
opposed to megabytes.

What is LAN
A Local Area Network (LAN) is a group of devices connected with various communications technologies in a small geographic
area. Ethernet is the most widely-used LAN technology. Communication on a LAN can either be with Peer-to-Peer devices or
Client-Server devices.

What is LCDUI
LCDUI is a shorthand way of referring to the MIDP user interface APIs, contained in the javax.microedition.lcdui package.
Strictly speaking, LCDUI stands for Liquid Crystal Display User Interface. It's a user interface toolkit for small device
screens which are commonly LCD screens.

What is MExE
The Mobile Execution Environment (MExE) is a specification created by the 3GPP which details an applicatio n environment for
next generation mobile devices. MExE consists of a variety of technologies including WAP, J2ME, CLDC and MIDP.

What is MIDlet
A MIDlet is an application written for MIDP. MIDlet applications are subclasses of the javax.microedition.midlet.MIDlet class
that is defined by MIDP.

What is MIDlet suite
MIDlets are packaged and distributed as MIDlet suites. A MIDlet suite can contain one or more MIDlets. The MIDlet suite
consists of two files, an application descriptor file with a .jad extension and an archive file with a .jar file. The
descriptor lists the archive file name, the names and class names for each MIDlet in the suite, and other information. The
archive file contains the MIDlet classes and resource files.

What is MIDP
The Mobile Information Device Profile (MIDP) is a specification for a J2ME profile. It is layered on top of CLDC and adds
APIs for application life cycle, user interface, networking, and persistent storage.

What is MIDP-NG
The Next Generation MIDP specification is currently under development by the Java Community Process. Planned improvements
include XML parsing and cryptographic support.

What is Mobitex
Mobitex is a packet-switched, narrowband PCS network, designed for wide-area wireless data communications. It was developed
in 1984 by Eritel, an Ericsson subsidiary, a nd there are now over 30 Mobitex networks in operation worldwide.

What is Modulation
Modulation is the method by which a high-frequency digital signal is grafted onto a lower-frequency analog wave, so that
digital packets are able to ride piggyback on the analog airwave.

What is MSC
A Mobile Switching Center (MSC) is a unit within a cellular phone network that automatically coordinates and switches calls
in a given cell. It monitors each caller's signal strength, and when a signal begins to fade, it hands off the call to
another MSC that's better positioned to manage the call.

What is Obfuscation
Obfuscation is a technique used to complicate code. Obfuscation makes code harder to understand when it is de-compiled, but
it typically has no affect on the functionality of the code. Obfuscation programs can be used to protect Java programs by
making them harder to reverse-engineer.

What is optional package
An optional package is a set of J2ME APIs providing services in a specific area, such as database access or multimedia.
Unlike a profile, it does not define a complete application environment, but rather is used in conjunction with a
configuration or a profile. It extends the runtime environment to support device capabilities that are not universal enough
to be defined as part of a profile or that need to be shared by different profiles. J2ME RMI and the Mobile Media RMI are
examples of optional packages.

What is OTA
Over The Air (OTA) refers to any wireless networking technology.

What is PCS
Personal Communications Service (PCS) is a suite of second-generation, digitally modulated mobile-communications interfaces
that includes TDMA, CDMA, and GSM. PCS serves as an umbrella term for second-generation wireless technologies operating in
the 1900MHz range

What is PDAP
The Personal Digital Assistant Profile (PDAP) is a J2ME profile specification designed for small platforms such as PalmOS
devices. You can think of PDAs as being larger than mobile phones but smaller than set-top boxes. PDAP is built on top of
CLDC and will specify user interface and persistent storage APIs. PDAP is currently being developed using the Java Community
Process (JCP).

What is PDC
Personal Digital Cellular (PDC) is a Japanese standard for wireless communications.

What is PDCP
Parallel and Distributed Computing Practices (PDCP) are often used to describe computer systems that are spread over many
devices on a network (wired or wireless) where many nodes process data simultaneously.

What is Personal Profile
The Personal Profile is a J2ME profile specification. Layered on the Foundation Profile and CDC, the Personal Profile will be
the next generation of PersonalJava technology. The specification is currently in development under the Java Community
Process (JCP).

What is PersonalJava
PersonalJava is a Java environment based on the Java virtual machine1 (JVM) and a set of APIs similar to a JDK 1.1
environment. It includes the Touchable Look and Feel (also called Truffle), a graphic toolkit that is optimized for consumer
devices with a touch sensitive screen. PersonalJava will be included in J2ME in the upcoming Personal Profile, which is built
on CDC.

What is PNG
Portable Network Graphics (PNG) is an image format offering lossless compression and storage flexibility. The MIDP
specification requires implementations to recognize certain types of PNG images.

What is POSE
Palm OS Emulator (POSE).

What is PRC
Palm Resource Code (PRC) is the file format for Palm OS applications.

What is preverification
Due to memory and processing power available on a device, the verification process of classes are split into two processes.
The first process is the preverification which is off-device and done using the preverify tool. The second process is
verification which is done on-device.

What is profile
A profile is a set of APIs added to a configuration to support specific uses of a mobile device. Along with its underlying
configuration, a profile defines a complete, and usually self-contained, general-purpose application environment. Profiles
often, but not always, define APIs for user interface and persistence; the MIDP profile, based on the CLDC configuration,
fits this pattern. Profiles may be supersets or subsets of other profiles; the Personal Basis Profile is a subset of the
Personal Profile and a superset of the Foundation Profile. See also configuration, optional package.

What is Provisioning
In telecommunications terms, provisioning means to provide telecommunications services to a user. This includes providing all
necessary hardware, software, and wiring or transmission devices.

What is PSTN
The public service telephone network (PSTN) is the traditional, land-line based system for exchanging phone calls.

What is RMI
Remote method invocation (RMI) is a feature of J2SE that enables Java objects running in one virtual machine to invoke
methods of Java objects running in another virtual machine, seamlessly.

What is RMI OP
The RMI Optional Package (RMI OP) is a subset of J2SE 1.3's RMI functionality used in CDC-based profiles that incorporate the
Foundation Profile, such as the Personal Basis Profile and the Personal Profile. The RMIOP cannot be used with CLDC-based
profiles because they lack object serialization and other important features found only in CDC-based profiles. RMIOP supports
most of the J2SE RMI functionality, including the Java Remote Method Protocol, marshalled objects, distributed garbage
collection, registry-based object lookup, and network class loading, but not HTTP tunneling or the Java 1.1 stub protocol.

What is RMI Profile
The RMI Profile is a J2ME profile specification designed to support Java's Remote Method Invocation (RMI) distributed object
system. Devices implementing the RMI Profile will be able to interoperate via RMI with other Java devices, including Java 2,
Standard Edition. The RMI Profile is based on the Foundation Profile, which in turn is based on CDC.

What is RMS
The Record Management System (RMS) is a simple record-oriented database that allows a MIDlet to persistently store
information and retrieve it later. Different MIDlets can also use the RMS to share data.

What is SDK
A Software Development Kit (SDK) is a set of tools used to develop applications for a particular platform. An SDK typically
contains a compiler, linker, and debugger. It may also contain libraries and documentation for APIs.

What is SIM
A Subscriber Identity Module (SIM) is a stripped-down smart card containing information about the identity of a cell-phone
subscriber, and subscriber authentication and service information. Because the SIM uniquely identifies the subscriber and is
portable among handsets, the user can move it from one kind of phone to another, facilitating international roaming.

What is SMS
Short Message Service (SMS) is a point-to-point service similar to paging for sending text messages of up to 160 characters
to mobile phones.

What is SOAP
The Simple Object Access Protocol (SOAP) is an XML- based protocol that allows objects of any type to communicated in a
distributed environment. SOAP is used in developing Web Services.

What is SSL
Secure Sockets Layer (SSL) is a socket protocol that encrypts data sent over the network and provides authentication for the
socket endpoints.

What is T9
T9 is a text input method for mobile phones and other small devices. It replaces the "multi-tap" input method by guessing the
word that you are trying to enter. T9 may be embedded in a device by the manufacturer. Note that even if the device supports
T9, the Java implementation may or may not use it. Check your documentation for details.

What is TDMA
Time Division Multiple Access (TDMA) is a second-generation modulation standard using bandwidth allocated in the 800 MHz, 900
MHz, and 1900MHz ranges.

What is Telematics
Telematics is a location-based service that routes event notification and control data over wireless networks to and from
mobile devices installed in automobiles. Telematics makes use of GPS technology to track vehicle latitude and longitude, and
displays maps in LED consoles mounted in dashboards. It connects to remote processing centers that turn provide server-side
Internet and voice services, as well as access to database resources.

What is Tomcat
Tomcat is a reference implementation of the Java servlet and JavaServer Pages (JSP) specifications. It is intended as a
platform for developing and testing servlets.

What is UDDI
Universal Description, Discovery, and Integration (UDDI) is an XML-based standard for describing, publishing, and finding Web
services. UDDI is a specification for a distributed registry of Web services.

What is UMTS
Developed by Nortel Networks, Universal Mobile Telecommunications Service (UMTS) is a standard that will provide cellular
users a consistent set of technologies no matter where they are located worldwide. UMTS utilizes W-CDMA technology.

What is VLR
The Visitor Location Register (VLR) is a database that contains temporary information about subscribers.

What is WAE
The Wireless Application Environment (WAE) provides a application framework for small devices. WAE leverages other
technologies such as WAP, WTP, and WSP.

What is WAP
Wireless Application Protocol (WAP) is a protocol for transmitting data between servers and clients (usually small wireless
devices like mobile phones). WAP is analogous to HTTP in the World Wide Web. Many mobile phones include WAP browser software
to allow users access to Internet WAP sites.

What is WAP Gateway
A WAP Gateway acts as a bridge allowing WAP devices to communicate with other networks (namely the Internet).

What is W-CDMA
Wideband Code-Division Multiple Access (W-CDMA), also known as IMT-2000, is a 3rd generation wireless technology. Supports
speeds up to 384Kbps on a wide-area network, or 2Mbps locally.

What is WDP
Wireless Datagram Protocol (WDP) works as the transport layer of WAP. WDP processes datagrams from upper layers to formats
required by different physical datapaths, bearers, that may be for example GSM SMS or CDMA Packet Data. WDP is adapted to the
bearers available in the device so upper layers don't need to care about the physical level.

What is WMA
The Wireless Messaging API (WMA) is a set of classes for sending and receiving Short Message Service messages. See also SMS.

What is WML
The Wireless Markup Language (WML) is a simple language used to create applications for small wireless devices like mobile
phones. WML is analogous to HTML in the World Wide Web.

What is WMLScript
WMLScript is a subset of the JavaScript scripting language designed as part of the WAP standard to provide a convenient
mechanism to access mobile phone's peripheral functions.

What is WSP
Wireless Session Protocol (WSP) implements session services of WAP. Sessions can be connection-oriented and connectionless
and they may be suspended and resumed at will.

What is WTLS
Wireless Transport Layer Security protocal (WTLS) does all cryptography oriented features of WAP. WTLS handles
encryption/decryption, user authentication and data integrity. WTLS is based on the fixed network Transport Layer Security
protocal (TLS), formerly known as Secure Sockets Layer (SSL).

What is WTP
Wireless Transaction Protocol (WTP) is WAP's transaction protocol that works between the session protocol WSP and security
protocol WTLS. WTP chops data packets into lower level datagrams and concatenates received datagrams into useful data. WTP
also keeps track of received and sent packets and does re-transmissions and acknowledgment sending when needed.

Java Interview Questions

Q1. How could Java classes direct program messages to the system console, but error messages, say to a file?

A. The class System has a variable out that represents the standard output, and the variable err that represents the standard error device. By default, they both point at the system console. This how the standard output and error could be re-directed:

PrintStream st = new PrintStream(new FileOutputStream("output.txt")); System.setErr(st); System.setOut(st);

Q2. What's the difference between an interface and an abstract class?

A. An abstract class may contain code in method bodies, which is not allowed in an interface. Java does not allow inheritance from multiple classes. On the other hand, you can implement multiple interfaces in your class. Also, an abstract class can contain private and protected members, and non-static member variables.

Q3. Why would you use a synchronized block vs. synchronized method?

A. Synchronized blocks place locks for shorter periods than synchronized methods, increasing the possibility of concurrent access to the protected code.

Q4. Explain the usage of the keyword transient?

A. This keyword indicates that the value of this member variable is not serialized with the object. When the class will be de-serialized, this variable will be initialized with a default value of its data type (e.g. zero for integers).

Q5. How can you force garbage collection?

A. You can't force GC, but could request it by calling System.gc(). JVM does not guarantee that GC will be started immediately, if at all.

Q6. How do you know if an explicit object casting is needed?

A. You can use an object anywhere it's declared class or a super-class is expected. You have to cast if a sub-class is expected, e.g. if you want to assign to a sub-class object or to use a sub-class's method.

Q7. What's the difference between the methods sleep() and wait()

A. The code sleep(1000) suspends the thread for at least one second. The code wait(1000), causes a wait of at most one second. A thread could stop waiting earlier if it receives the notify() or notifyAll() call. The method wait() is defined in the class Object and the method sleep() is defined in the class Thread.

Q8. Can you write a Java class that could be used both as an applet as well as an application?

A. Yes. Add a main() method to the applet's class.

Q9. What's the difference between constructors and other methods?

A. Constructors must have the same name as the class and can not return a value. They are only called once for a given object while regular methods could be called many times.

Q10. Can you call one constructor from another if a class has multiple constructors

A. Yes. Use this() syntax, passing any required parameters.

Q11. Explain the usage of Java packages.

A. This is a way to organize files when a project consists of multiple modules. It also helps resolve naming conflicts when different packages have classes with the same names. Package-private access level also allows you to protect data from being used by the non-authorized classes.

Q12. If a class is located in a package, what do you need to change in the OS environment to be able to use it?

A. You need to add a directory or a jar file that contains the package directories to the CLASSPATH environment variable. Let's say a class Employee belongs to a package com.xyz.hr; and is located in the file c:\dev\com\xyz\hr\Employee.java. In this case, you'd need to add c:\dev to the variable CLASSPATH. If this class contains the method main(), you could test it from a command prompt window as follows:

c:\>java com.xyz.hr.Employee

Alternatively you can pass the classpath as a parameter to the JRE, e.g. java -cp "the-classpath"

Q13. What's the difference between J2SDK 1.5 and J2SDK 5.0?

A.There's no difference, Sun Microsystems just re-branded this version.

Q14. What would you use to compare two String variables - the operator == or the method equals()?

A. I'd use the method equals() to compare the values of the Strings and the == to check if two variables point at the same instance of a String object.

Q15. Does it matter in what order catch statements for FileNotFoundException and IOExceptipon are written?

A. Yes, it does. The FileNoFoundException is inherited from the IOException. Exception's subclasses should be caught first, otherwise the super-class catch will hide the sub-class.

Q16. Can an inner class declared inside of a method access local variables of this method?

A. It's possible if these variables are final.

Q17. What can go wrong if you replace && with & in the following code:

String a=null; if (a!=null && a.length()>10) {...}

A. A single ampersand here would lead to a NullPointerException.

Q18. What's the main difference between a Vector and an ArrayList

A. Java Vector class is internally synchronized and ArrayList is not.

Q19. When should the method invokeLater()be used?

A. This method is used to ensure that the Runnable passed to invokeLater() is executed on the event-dispatching thread.

Q20. How can a subclass call a method or a constructor defined in a superclass?

A. Use the following syntax: super.myMethod(); To call a constructor of the superclass, just call super() in the first line of the subclass's constructor, passing any required parameters.

For senior-level developers:

Q21. What's the difference between a queue and a stack?

A. Stacks works by last-in-first-out rule (LIFO), while queues use the FIFO (first-in, first-out) rule.

Q22. You can create an abstract class that contains only abstract methods. On the other hand, you can create an interface that declares the same methods. So can you use abstract classes instead of interfaces?

A. Yes, but abstract classes are more limited because a class can only extend one class but can implement multiple interfaces.

Q23. What comes to mind when you hear about a young generation in Java?

A. Garbage collection; a young generation is a recent collection of newly created objects, which is reclaimed more aggressively than older ones.

Q24. What comes to mind when someone mentions a shallow copy in Java?

A. Object cloning; a shallow copy reuses references to the original's member variables, but a (complete) deep copy clones the entire object tree.

Q25. If you're overriding the method equals() of an object, which other method you might also consider?

A. hashCode(), because the hash algorithm should use the same member variables as equals().

Q26. You are planning to do an indexed search in a list of objects. Which of the two Java collections should you use:
ArrayList or LinkedList?

A. ArrayList

Q27. How would you make a copy of an entire Java object with its state?

A. Have this class implement Cloneable interface and call its method clone().

Q28. How can you minimize the need of garbage collection and make the memory use more effective?

A. Use object pooling to avoid creating new objects and weak object references to avoid keeping objects in memory that you can cheaply reconstruct.

Q29. There are two classes: A and B. The class B needs to inform a class A when some important event has happened. What Java technique would you use to implement it?

A. If these classes are threads I'd consider notify() or notifyAll(). For regular classes you can use the Observer interface. or some other implementation of the Listener pattern.

Q30. What access level do you need to specify in the class declaration to ensure that only classes from the same directory can access it?

A. You do not need to specify any access level, and Java will use a default package-private access level.

J2EE Interview Questions

What is abstract schema

The part of an entity bean's deployment descriptor that defines the bean's persistent fields and relationships.

What is abstract schema name

A logical name that is referenced in EJB QL queries.

What is access control

The methods by which interactions with resources are limited to collections of users or programs for the purpose of enforcing

integrity, confidentiality, or availability constraints.

What is ACID

The acronym for the four properties guaranteed by transactions: atomicity, consistency, isolation, and durability.

What is activation

The process of transferring an enterprise bean from secondary storage to memory. (See passivation.) What is anonymous access

Accessing a resource without authentication.

What is applet

A J2EE component that typically executes in a Web browser but can execute in a variety of other applications or devices that

support the applet programming model.

What is applet container

A container that includes support for the applet programming model.

What is application assembler

A person who combines J2EE components and modules into deployable application units.

What is application client

A first-tier J2EE client component that executes in its own Java virtual machine. Application clients have access to some

J2EE platform APIs.

What is application client container

A container that supports application client components. What is application client module

A software unit that consists of one or more classes and an application client deployment descriptor.

What is application component provider

A vendor that provides the Java classes that implement components' methods, JSP page definitions, and any required deployment

descriptors.

What is application configuration resource file

An XML file used to configure resources for a JavaServer Faces application, to define navigation rules for the application,

and to register converters, validators, listeners, renderers, and components with the application.

What is archiving

The process of saving the state of an object and restoring it.

What is asant

A Java-based build tool that can be extended using Java classes. The configuration files are XML-based, calling out a target

tree where various tasks get executed.

What is attribute

A qualifier on an XML tag that provides additional information.

What is authentication

The process that verifies the identity of a user, device, or other entity in a computer system, usually as a prerequisite to

allowing access to resources in a system. The Java servlet specification requires three types of authentication-basic,

form-based, and mutual-and supports digest authentication.

What is authorization

The process by which access to a method or resource is determined. Authorization depends on the determination of whether the

principal associated with a request through authentication is in a given security role. A security role is a logical grouping

of users defined by the person who assembles the application. A deployer maps security roles to security identities. Security

identities may be principals or groups in the operational environment.

What is authorization constraint

An authorization rule that determines who is permitted to access a Web resource collection.

What is B2B

B2B stands for Business-to-business.

What is backing bean

A JavaBeans component that corresponds to a JSP page that includes JavaServer Faces components. The backing bean defines

properties for the components on the page and methods that perform processing for the component. This processing includes

event handling, validation, and processing associated with navigation. What is basic authentication

An authentication mechanism in which a Web server authenticates an entity via a user name and password obtained using the Web

application's built-in authentication mechanism.

What is bean-managed persistence

The mechanism whereby data transfer between an entity bean's variables and a resource manager is managed by the entity bean.

What is bean-managed transaction

A transaction whose boundaries are defined by an enterprise bean.

What is binary entity

See unparsed entity.

What is binding (XML)

Generating the code needed to process a well-defined portion of XML data.

What is binding (JavaServer Faces technology)

Wiring UI components to back-end data sources such as backing bean properties.

What is build file

The XML file that contains one or more asant targets. A target is a set of tasks you want to be executed. When starting

asant, you can select which targets you want to have executed. When no target is given, the project's default target is

executed.

What is business logic

The code that implements the functionality of an application. In the Enterprise JavaBeans architecture, this logic is

implemented by the methods of an enterprise bean.

What is business method

A method of an enterprise bean that implements the business logic or rules of an application.

What is callback methods

Component methods called by the container to notify the component of important events in its life cycle.

What is caller

Same as caller principal.

What is caller principal

The principal that identifies the invoker of the enterprise bean method. What is cascade delete

A deletion that triggers another deletion. A cascade delete can be specified for an entity bean that has container-managed

persistence.

What is CDATA

A predefined XML tag for character data that means don't interpret these characters, as opposed to parsed character data

(PCDATA), in which the normal rules of XML syntax apply. CDATA sections are typically used to show examples of XML syntax.

What is certificate authority

A trusted organization that issues public key certificates and provides identification to the bearer.

What is client-certificate authentication

An authentication mechanism that uses HTTP over SSL, in which the server and, optionally, the client authenticate each other

with a public key certificate that conforms to a standard that is defined by X.509 Public Key Infrastructure.

What is comment

In an XML document, text that is ignored unless the parser is specifically told to recognize it.

What is commit

The point in a transaction when all updates to any resources involved in the transaction are made permanent.

What is component

See what is J2EE component.

What is component (JavaServer Faces technology)

See what is JavaServer Faces UI component.

What is component contract

The contract between a J2EE component and its container. The contract includes life-cycle management of the component, a

context interface that the instance uses to obtain various information and services from its container, and a list of

services that every container must provide for its components.

What is component-managed sign-on

A mechanism whereby security information needed for signing on to a resource is provided by an application component.

What is connection

See what is resource manager connection.

What is connection factory

See what is resource manager connection factory.

What is connector

A standard extension mechanism for containers that provides connectivity to enterprise information systems. A connector is

specific to an enterprise information system and consists of a resource adapter and application development tools for

enterprise information system connectivity. The resource adapter is plugged in to a container through its support for

system-level contracts defined in the Connector architecture.

What is Connector architecture

An architecture for integration of J2EE products with enterprise information systems. There are two parts to this

architecture: a resource adapter provided by an enterprise information system vendor and the J2EE product that allows this

resource adapter to plug in. This architecture defines a set of contracts that a resource adapter must support to plug in to

a J2EE product-for example, transactions, security, and resource management.

What is container

An entity that provides life-cycle management, security, deployment, and runtime services to J2EE components. Each type of

container (EJB, Web, JSP, servlet, applet, and application client) also provides component-specific services.

What is container-managed persistence

The mechanism whereby data transfer between an entity bean's variables and a resource manager is managed by the entity bean's

container.

What is container-managed sign-on

The mechanism whereby security information needed for signing on to a resource is supplied by the container.

What is container-managed transaction

A transaction whose boundaries are defined by an EJB container. An entity bean must use container-managed transactions.What is content

In an XML document, the part that occurs after the prolog, including the root element and everything it contains.

What is context attribute

An object bound into the context associated with a servlet.

What is context root

A name that gets mapped to the document root of a Web application.

What is conversational state

The field values of a session bean plus the transitive closure of the objects reachable from the bean's fields. The

transitive closure of a bean is defined in terms of the serialization protocol for the Java programming language, that is,

the fields that would be stored by serializing the bean instance.

What is CORBA

Common Object Request Broker Architecture. A language-independent distributed object model specified by the OMG.

What is create method

A method defined in the home interface and invoked by a client to create an enterprise bean.

What is credentials

The information describing the security attributes of a principal.

What is CSS

Cascading style sheet. A stylesheet used with HTML and XML documents to add a style to all elements marked with a particular

tag, for the direction of browsers or other presentation mechanisms.

What is CTS

Compatibility test suite. A suite of compatibility tests for verifying that a J2EE product complies with the J2EE platform

specification.

What is data

The contents of an element in an XML stream, generally used when the element does not contain any subelements. When it does,

the term content is generally used. When the only text in an XML structure is contained in simple elements and when elements

that have subelements have little or no data mixed in, then that structure is often thought of as XML data, as opposed to an

XML document.

What is DDP

Document-driven programming. The use of XML to define applications.

What is declaration

The very first thing in an XML document, which declares it as XML. The minimal declaration is . The

declaration is part of the document prolog.

What is declarative security

Mechanisms used in an application that are expressed in a declarative syntax in a deployment descriptor.

What is delegation

An act whereby one principal authorizes another principal to use its identity or privileges with some restrictions.

What is deployer

A person who installs J2EE modules and applications into an operational environment.

What is deployment

The process whereby software is installed into an operational environment.

What is deployment descriptor

An XML file provided with each module and J2EE application that describes how they should be deployed. The deployment

descriptor directs a deployment tool to deploy a module or application with specific container options and describes specific

configuration requirements that a deployer must resolve.

What is destination

A JMS administered object that encapsulates the identity of a JMS queue or topic. See point-to-point messaging system,

publish/subscribe messaging system.

What is digest authentication

An authentication mechanism in which a Web application authenticates itself to a Web server by sending the server a message

digest along with its HTTP request message. The digest is computed by employing a one-way hash algorithm to a concatenation

of the HTTP request message and the client's password. The digest is typically much smaller than the HTTP request and doesn't

contain the password.

What is distributed application

An application made up of distinct components running in separate runtime environments, usually on different platforms

connected via a network. Typical distributed applications are two-tier (client-server), three-tier

(client-middleware-server), and multitier (client-multiple middleware-multiple servers).

What is document

In general, an XML structure in which one or more elements contains text intermixed with subelements. See also data.

What is Document Object Model

An API for accessing and manipulating XML documents as tree structures. DOM provides platform-neutral, language-neutral

interfaces that enables programs and scripts to dynamically access and modify content and structure in XML documents.

What is document root

The top-level directory of a WAR. The document root is where JSP pages, client-side classes and archives, and static Web

resources are stored.

What is DTD

Document type definition. An optional part of the XML document prolog, as specified by the XML standard. The DTD specifies

constraints on the valid tags and tag sequences that can be in the document. The DTD has a number of shortcomings, however,

and this has led to various schema proposals. For example, the DTD entry says that the XML

element called username contains parsed character data-that is, text alone, with no other structural elements under it. The

DTD includes both the local subset, defined in the current file, and the external subset, which consists of the definitions

contained in external DTD files that are referenced in the local subset using a parameter entity.

What is durable subscription

In a JMS publish/subscribe messaging system, a subscription that continues to exist whether or not there is a current active

subscriber object. If there is no active subscriber, the JMS provider retains the subscription's messages until they are

received by the subscription or until they expire.

What is EAR file

Enterprise Archive file. A JAR archive that contains a J2EE application.

What is ebXML

Electronic Business XML. A group of specifications designed to enable enterprises to conduct business through the exchange of

XML-based messages. It is sponsored by OASIS and the United Nations Centre for the Facilitation of Procedures and Practices

in Administration, Commerce and Transport (U.N./CEFACT).

What is EJB

Enterprise JavaBeans.

What is EJB container

A container that implements the EJB component contract of the J2EE architecture. This contract specifies a runtime

environment for enterprise beans that includes security, concurrency, life-cycle management, transactions, deployment,

naming, and other services. An EJB container is provided by an EJB or J2EE server. What is EJB container provider

A vendor that supplies an EJB container.

What is EJB context

An object that allows an enterprise bean to invoke services provided by the container and to obtain the information about the

caller of a client-invoked method.

What is EJB home object

An object that provides the life-cycle operations (create, remove, find) for an enterprise bean. The class for the EJB home

object is generated by the container's deployment tools. The EJB home object implements the enterprise bean's home interface.

The client references an EJB home object to perform life-cycle operations on an EJB object. The client uses JNDI to locate an

EJB home object.

What is EJB JAR file

A JAR archive that contains an EJB module.

What is EJB module

A deployable unit that consists of one or more enterprise beans and an EJB deployment descriptor.

What is EJB object

An object whose class implements the enterprise bean's remote interface. A client never references an enterprise bean

instance directly; a client always references an EJB object. The class of an EJB object is generated by a container's

deployment tools.

What is EJB server

Software that provides services to an EJB container. For example, an EJB container typically relies on a transaction manager

that is part of the EJB server to perform the two-phase commit across all the participating resource managers. The J2EE

architecture assumes that an EJB container is hosted by an EJB server from the same vendor, so it does not specify the

contract between these two entities. An EJB server can host one or more EJB containers.

What is EJB server provider

A vendor that supplies an EJB server.

What is element

A unit of XML data, delimited by tags. An XML element can enclose other elements.

What is empty tag

A tag that does not enclose any content.

What is enterprise bean

A J2EE component that implements a business task or business entity and is hosted by an EJB container; either an entity bean,

a session bean, or a message-driven bean.

What is enterprise bean provider

An application developer who produces enterprise bean classes, remote and home interfaces, and deployment descriptor files,

and packages them in an EJB JAR file.

What is enterprise information system

The applications that constitute an enterprise's existing system for handling companywide information. These applications

provide an information infrastructure for an enterprise. An enterprise information system offers a well-defined set of

services to its clients. These services are exposed to clients as local or remote interfaces or both. Examples of enterprise

information systems include enterprise resource planning systems, mainframe transaction processing systems, and legacy

database systems.

What is enterprise information system resource

An entity that provides enterprise information system-specific functionality to its clients. Examples are a record or set of

records in a database system, a business object in an enterprise resource planning system, and a transaction program in a

transaction processing system.

What is Enterprise JavaBeans (EJB)

A component architecture for the development and deployment of object-oriented, distributed, enterprise-level applications.

Applications written using the Enterprise JavaBeans architecture are scalable, transactional, and secure.

What is Enterprise JavaBeans Query Language (EJB QL)

Defines the queries for the finder and select methods of an entity bean having container-managed persistence. A subset of

SQL92, EJB QL has extensions that allow navigation over the relationships defined in an entity bean's abstract schema.

What is an entity

A distinct, individual item that can be included in an XML document by referencing it. Such an entity reference can name an

entity as small as a character (for example, <, which references the less-than symbol or left angle bracket, <). An entity

reference can also reference an entire document, an external entity, or a collection of DTD definitions.

What is entity bean

An enterprise bean that represents persistent data maintained in a database. An entity bean can manage its own persistence or

can delegate this function to its container. An entity bean is identified by a primary key. If the container in which an

entity bean is hosted crashes, the entity bean, its primary key, and any remote references survive the crash.

What is entity reference

A reference to an entity that is substituted for the reference when the XML document is parsed. It can reference a predefined

entity such as < or reference one that is defined in the DTD. In the XML data, the reference could be to an entity that is

defined in the local subset of the DTD or to an external XML file (an external entity). The DTD can also carve out a segment

of DTD specifications and give it a name so that it can be reused (included) at multiple points in the DTD by defining a

parameter entity.

What is error

A SAX parsing error is generally a validation error; in other words, it occurs when an XML document is not valid, although it

can also occur if the declaration specifies an XML version that the parser cannot handle. See also fatal error, warning.

What is Extensible Markup Language

XML.

What is external entity

An entity that exists as an external XML file, which is included in the XML document using an entity reference.

What is external subset

That part of a DTD that is defined by references to external DTD files.

What is fatal error

A fatal error occurs in the SAX parser when a document is not well formed or otherwise cannot be processed. See also error,

warning.

What is filter

An object that can transform the header or content (or both) of a request or response. Filters differ from Web components in

that they usually do not themselves create responses but rather modify or adapt the requests for a resource, and modify or

adapt responses from a resource. A filter should not have any dependencies on a Web resource for which it is acting as a

filter so that it can be composable with more than one type of Web resource.

What is filter chain

A concatenation of XSLT transformations in which the output of one transformation becomes the input of the next.

What is finder method

A method defined in the home interface and invoked by a client to locate an entity bean.

What is form-based authentication

An authentication mechanism in which a Web container provides an application-specific form for logging in. This form of

authentication uses Base64 encoding and can expose user names and passwords unless all connections are over SSL.

What is general entity

An entity that is referenced as part of an XML document's content, as distinct from a parameter entity, which is referenced

in the DTD. A general entity can be a parsed entity or an unparsed entity.

What is group

An authenticated set of users classified by common traits such as job title or customer profile. Groups are also associated

with a set of roles, and every user that is a member of a group inherits all the roles assigned to that group.

What is handle

An object that identifies an enterprise bean. A client can serialize the handle and then later deserialize it to obtain a

reference to the enterprise bean. What is home handle

An object that can be used to obtain a reference to the home interface. A home handle can be serialized and written to stable

storage and deserialized to obtain the reference.

What is home interface

One of two interfaces for an enterprise bean. The home interface defines zero or more methods for managing an enterprise

bean. The home interface of a session bean defines create and remove methods, whereas the home interface of an entity bean

defines create, finder, and remove methods.

What is HTML

Hypertext Markup Language. A markup language for hypertext documents on the Internet. HTML enables the embedding of images,

sounds, video streams, form fields, references to other objects with URLs, and basic text formatting.

What is HTTP

Hypertext Transfer Protocol. The Internet protocol used to retrieve hypertext objects from remote hosts. HTTP messages

consist of requests from client to server and responses from server to client.

What is HTTPS

HTTP layered over the SSL protocol.

What is IDL

Interface Definition Language. A language used to define interfaces to remote CORBA objects. The interfaces are independent

of operating systems and programming languages.

What is IIOP

Internet Inter-ORB Protocol. A protocol used for communication between CORBA object request brokers.

What is impersonation

An act whereby one entity assumes the identity and privileges of another entity without restrictions and without any

indication visible to the recipients of the impersonator's calls that delegation has taken place. Impersonation is a case of

simple delegation. What is initialization parameter

A parameter that initializes the context associated with a servlet.

What is ISO 3166

The international standard for country codes maintained by the International Organization for Standardization (ISO).

What is ISV

Independent software vendor.

What is J2EE

Java 2 Platform, Enterprise Edition.

What is J2EE application

Any deployable unit of J2EE functionality. This can be a single J2EE module or a group of modules packaged into an EAR file along with a J2EE application deployment descriptor. J2EE applications are typically engineered to be distributed across multiple computing tiers.

What is J2EE component

A self-contained functional software unit supported by a container and configurable at deployment time. The J2EE specification defines the following J2EE components:

Application clients and applets are components that run on the client.

Java servlet and JavaServer Pages (JSP) technology components are Web components that run on the server.

Enterprise JavaBeans (EJB) components (enterprise beans) are business components that run on the server.

J2EE components are written in the Java programming language and are compiled in the same way as any program in the language. The difference between J2EE components and standard Java classes is that J2EE components are assembled into a J2EE application, verified to be well formed and in compliance with the J2EE specification, and deployed to production, where they are run and managed by the J2EE server or client container.

What is J2EE module

A software unit that consists of one or more J2EE components of the same container type and one deployment descriptor of that type. There are four types of modules: EJB, Web, application client, and resource adapter. Modules can be deployed as stand-alone units or can be assembled into a J2EE application.

What is J2EE product

An implementation that conforms to the J2EE platform specification.

What is J2EE product provider

A vendor that supplies a J2EE product.

What is J2EE server

The runtime portion of a J2EE product. A J2EE server provides EJB or Web containers or both.

What is J2ME

Abbreviate of Java 2 Platform, Micro Edition.

What is J2SE

Abbreviate of Java 2 Platform, Standard Edition.

What is JAR

Java archive. A platform-independent file format that permits many files to be aggregated into one file. What is Java 2 Platform, Enterprise Edition (J2EE)

An environment for developing and deploying enterprise applications. The J2EE platform consists of a set of services, application programming interfaces (APIs), and protocols that provide the functionality for developing multitiered, Web-based applications.

What is Java 2 Platform, Micro Edition (J2ME)

A highly optimized Java runtime environment targeting a wide range of consumer products, including pagers, cellular phones, screen phones, digital set-top boxes, and car navigation systems.

What is Java 2 Platform, Standard Edition (J2SE)

The core Java technology platform.

What is Java API for XML Processing (JAXP)

An API for processing XML documents. JAXP leverages the parser standards SAX and DOM so that you can choose to parse your data as a stream of events or to build a tree-structured representation of it. JAXP supports the XSLT standard, giving you control over the presentation of the data and enabling you to convert the data to other XML documents or to other formats, such as HTML. JAXP provides namespace support, allowing you to work with schema that might otherwise have naming conflicts.

What is Java API for XML Registries (JAXR)

An API for accessing various kinds of XML registries.

What is Java API for XML-based RPC (JAX-RPC)

An API for building Web services and clients that use remote procedure calls and XML.

What is Java IDL

A technology that provides CORBA interoperability and connectivity capabilities for the J2EE platform. These capabilities enable J2EE applications to invoke operations on remote network services using the Object Management Group IDL and IIOP.

What is Java Message Service (JMS)

An API for invoking operations on enterprise messaging systems.

What is Java Naming and Directory Interface (JNDI)

An API that provides naming and directory functionality.

What is Java Secure Socket Extension (JSSE)

A set of packages that enable secure Internet communications.

What is Java Transaction API (JTA)

An API that allows applications and J2EE servers to access transactions.

What is Java Transaction Service (JTS)

Specifies the implementation of a transaction manager that supports JTA and implements the Java mapping of the Object Management Group Object Transaction Service 1.1 specification at the level below the API.

What is JavaBeans component

A Java class that can be manipulated by tools and composed into applications. A JavaBeans component must adhere to certain property and event interface conventions.

What is JavaMail

An API for sending and receiving email.

What is JavaServer Faces Technology

A framework for building server-side user interfaces for Web applications written in the Java programming language.

What is JavaServer Faces conversion model

A mechanism for converting between string-based markup generated by JavaServer Faces UI components and server-side Java objects.

What is JavaServer Faces event and listener model

A mechanism for determining how events emitted by JavaServer Faces UI components are handled. This model is based on the JavaBeans component event and listener model.

What is JavaServer Faces expression language

A simple expression language used by a JavaServer Faces UI component tag attributes to bind the associated component to a bean property or to bind the associated component's value to a method or an external data source, such as a bean property. Unlike JSP EL expressions, JavaServer Faces EL expressions are evaluated by the JavaServer Faces implementation rather than by the Web container.

What is JavaServer Faces navigation model

A mechanism for defining the sequence in which pages in a JavaServer Faces application are displayed.

What is JavaServer Faces UI component

A user interface control that outputs data to a client or allows a user to input data to a JavaServer Faces application.

What is JavaServer Faces UI component class

A JavaServer Faces class that defines the behavior and properties of a JavaServer Faces UI component.

What is JavaServer Faces validation model

A mechanism for validating the data a user inputs to a JavaServer Faces UI component.

What is JavaServer Pages (JSP)

An extensible Web technology that uses static data, JSP elements, and server-side Java objects to generate dynamic content for a client. Typically the static data is HTML or XML elements, and in many cases the client is a Web browser.

What is JavaServer Pages Standard Tag Library (JSTL)

A tag library that encapsulates core functionality common to many JSP applications. JSTL has support for common, structural tasks such as iteration and conditionals, tags for manipulating XML documents, internationalization and locale-specific formatting tags, SQL tags, and functions.

What is JAXR client

A client program that uses the JAXR API to access a business registry via a JAXR provider.

What is JAXR provider

An implementation of the JAXR API that provides access to a specific registry provider or to a class of registry providers that are based on a common specification.

What is JDBC

An API for database-independent connectivity between the J2EE platform and a wide range of data sources.

What is JMS

Java Message Service.

What is JMS administered object

A preconfigured JMS object (a resource manager connection factory or a destination) created by an administrator for the use of JMS clients and placed in a JNDI namespace.

What is JMS application

One or more JMS clients that exchange messages.

What is JMS client

A Java language program that sends or receives messages.

What is JMS provider

A messaging system that implements the Java Message Service as well as other administrative and control functionality needed in a full-featured messaging product.

What is JMS session

A single-threaded context for sending and receiving JMS messages. A JMS session can be nontransacted, locally transacted, or participating in a distributed transaction.

What is JNDI

Abbreviate of Java Naming and Directory Interface.

What is JSP

Abbreviate of JavaServer Pages.

What is JSP action

A JSP element that can act on implicit objects and other server-side objects or can define new scripting variables. Actions follow the XML syntax for elements, with a start tag, a body, and an end tag; if the body is empty it can also use the empty tag syntax. The tag must use a prefix. There are standard and custom actions.

What is JSP container

A container that provides the same services as a servlet container and an engine that interprets and processes JSP pages into a servlet.

What is JSP container, distributed

A JSP container that can run a Web application that is tagged as distributable and is spread across multiple Java virtual machines that might be running on different hosts.

What is JSP custom action

A user-defined action described in a portable manner by a tag library descriptor and imported into a JSP page by a taglib directive. Custom actions are used to encapsulate recurring tasks in writing JSP pages.

What is JSP custom tag

A tag that references a JSP custom action.

What is JSP declaration

A JSP scripting element that declares methods, variables, or both in a JSP page.

What is JSP directive

A JSP element that gives an instruction to the JSP container and is interpreted at translation time.

What is JSP document

A JSP page written in XML syntax and subject to the constraints of XML documents.

What is JSP element

A portion of a JSP page that is recognized by a JSP translator. An element can be a directive, an action, or a scripting element.

What is JSP expression

A scripting element that contains a valid scripting language expression that is evaluated, converted to a String, and placed into the implicit out object.

What is JSP expression language

A language used to write expressions that access the properties of JavaBeans components. EL expressions can be used in static text and in any standard or custom tag attribute that can accept an expression.

What is JSP page

A text-based document containing static text and JSP elements that describes how to process a request to create a response. A JSP page is translated into and handles requests as a servlet.

What is JSP scripting element

A JSP declaration, scriptlet, or expression whose syntax is defined by the JSP specification and whose content is written according to the scripting language used in the JSP page. The JSP specification describes the syntax and semantics for the case where the language page attribute is java.

What is JSP scriptlet

A JSP scripting element containing any code fragment that is valid in the scripting language used in the JSP page. The JSP specification describes what is a valid scriptlet for the case where the language page attribute is java.

What is JSP standard action

An action that is defined in the JSP specification and is always available to a JSP page.

What is JSP tag file

A source file containing a reusable fragment of JSP code that is translated into a tag handler when a JSP page is translated into a servlet.

What is JSP tag handler

A Java programming language object that implements the behavior of a custom tag.

What is JSP tag library

A collection of custom tags described via a tag library descriptor and Java classes.

What is JSTL

Abbreviate of JavaServer Pages Standard Tag Library.

What is JTA

Abbreviate of Java Transaction API.

What is JTS

Abbreviate of Java Transaction Service.

What is keystore

A file containing the keys and certificates used for authentication. What is life cycle (J2EE component)

The framework events of a J2EE component's existence. Each type of component has defining events that mark its transition into states in which it has varying availability for use. For example, a servlet is created and has its init method called by its container before invocation of its service method by clients or other servlets that require its functionality. After the call of its init method, it has the data and readiness for its intended use. The servlet's destroy method is called by its container before the ending of its existence so that processing associated with winding up can be done and resources can be released. The init and destroy methods in this example are callback methods. Similar considerations apply to the life cycle of all J2EE component types: enterprise beans, Web components (servlets or JSP pages), applets, and application clients.

What is life cycle (JavaServer Faces)

A set of phases during which a request for a page is received, a UI component tree representing the page is processed, and a response is produced. During the phases of the life cycle:

The local data of the components is updated with the values contained in the request parameters.

Events generated by the components are processed.

Validators and converters registered on the components are processed.

The components' local data is updated to back-end objects.

The response is rendered to the client while the component state of the response is saved on the server for future requests.

What is local subset

That part of the DTD that is defined within the current XML file.

What is managed bean creation facility

A mechanism for defining the characteristics of JavaBeans components used in a JavaServer Faces application.

What is message

In the Java Message Service, an asynchronous request, report, or event that is created, sent, and consumed by an enterprise application and not by a human. It contains vital information needed to coordinate enterprise applications, in the form of precisely formatted data that describes specific business actions.

What is message consumer

An object created by a JMS session that is used for receiving messages sent to a destination.

What is message-driven bean

An enterprise bean that is an asynchronous message consumer. A message-driven bean has no state for a specific client, but its instance variables can contain state across the handling of client messages, including an open database connection and an object reference to an EJB object. A client accesses a message-driven bean by sending messages to the destination for which the bean is a message listener.

What is message producer

An object created by a JMS session that is used for sending messages to a destination.

What is mixed-content model

A DTD specification that defines an element as containing a mixture of text and one more other elements. The specification must start with #PCDATA, followed by diverse elements, and must end with the zero-or-more asterisk symbol (*).

What is method-binding expression

A JavaServer Faces EL expression that refers to a method of a backing bean. This method performs either event handling, validation, or navigation processing for the UI component whose tag uses the method-binding expression.

What is method permission

An authorization rule that determines who is permitted to execute one or more enterprise bean methods.

What is mutual authentication

An authentication mechanism employed by two parties for the purpose of proving each other's identity to one another.

What is namespace

A standard that lets you specify a unique label for the set of element names defined by a DTD. A document using that DTD can be included in any other document without having a conflict between element names. The elements defined in your DTD are then uniquely identified so that, for example, the parser can tell when an element should be interpreted according to your DTD rather than using the definition for an element in a different DTD.

What is naming context

A set of associations between unique, atomic, people-friendly identifiers and objects.

What is naming environment

A mechanism that allows a component to be customized without the need to access or change the component's source code. A container implements the component's naming environment and provides it to the component as a JNDI naming context. Each component names and accesses its environment entries using the java:comp/env JNDI context. The environment entries are declaratively specified in the component's deployment descriptor.

What is normalization

The process of removing redundancy by modularizing, as with subroutines, and of removing superfluous differences by reducing them to a common denominator. For example, line endings from different systems are normalized by reducing them to a single new line, and multiple whitespace characters are normalized to one space.

What is North American Industry Classification System (NAICS)

A system for classifying business establishments based on the processes they use to produce goods or services.

What is notation

A mechanism for defining a data format for a non-XML document referenced as an unparsed entity. This is a holdover from SGML. A newer standard is to use MIME data types and namespaces to prevent naming conflicts.

What is OASIS

Organization for the Advancement of Structured Information Standards. A consortium that drives the development, convergence, and adoption of e-business standards. Its Web site is http://www.oasis-open.org/. The DTD repository it sponsors is at http://www.XML.org.

What is OMG

Object Management Group. A consortium that produces and maintains computer industry specifications for interoperable enterprise applications. Its Web site is http://www.omg.org/.

What is one-way messaging

A method of transmitting messages without having to block until a response is received.

What is ORB

Object request broker. A library that enables CORBA objects to locate and communicate with one another. What is OS principal

A principal native to the operating system on which the J2EE platform is executing.

What is OTS

Object Transaction Service. A definition of the interfaces that permit CORBA objects to participate in transactions.

What is parameter entity

An entity that consists of DTD specifications, as distinct from a general entity. A parameter entity defined in the DTD can then be referenced at other points, thereby eliminating the need to recode the definition at each location it is used.

What is parsed entity

A general entity that contains XML and therefore is parsed when inserted into the XML document, as opposed to an unparsed entity.

What is parser

A module that reads in XML data from an input source and breaks it into chunks so that your program knows when it is working with a tag, an attribute, or element data. A nonvalidating parser ensures that the XML data is well formed but does not verify that it is valid. See also validating parser.

What is passivation

The process of transferring an enterprise bean from memory to secondary storage. See activation.

What is persistence

The protocol for transferring the state of an entity bean between its instance variables and an underlying database.

What is persistent field

A virtual field of an entity bean that has container-managed persistence; it is stored in a database.

What is POA

Portable Object Adapter. A CORBA standard for building server-side applications that are portable across heterogeneous ORBs.

What is point-to-point messaging system

A messaging system built on the concept of message queues. Each message is addressed to a specific queue; clients extract messages from the queues established to hold their messages.

What is primary key

An object that uniquely identifies an entity bean within a home.

What is principal

The identity assigned to a user as a result of authentication.

What is privilege

A security attribute that does not have the property of uniqueness and that can be shared by many principals.

What is processing instruction

Information contained in an XML structure that is intended to be interpreted by a specific application.

What is programmatic security

Security decisions that are made by security-aware applications. Programmatic security is useful when declarative security alone is not sufficient to express the security model of an application.

What is prolog

The part of an XML document that precedes the XML data. The prolog includes the declaration and an optional DTD.

What is public key certificate

Used in client-certificate authentication to enable the server, and optionally the client, to authenticate each other. The public key certificate is the digital equivalent of a passport. It is issued by a trusted organization, called a certificate authority, and provides identification for the bearer.

What is publish/subscribe messaging system

A messaging system in which clients address messages to a specific node in a content hierarchy, called a topic. Publishers and subscribers are generally anonymous and can dynamically publish or subscribe to the content hierarchy. The system takes care of distributing the messages arriving from a node's multiple publishers to its multiple subscribers.

What is query string

A component of an HTTP request URL that contains a set of parameters and values that affect the handling of the request.

What is queue

See point-to-point messaging system.

What is RAR

Resource Adapter Archive. A JAR archive that contains a resource adapter module.

What is RDF

Resource Description Framework. A standard for defining the kind of data that an XML file contains. Such information can help ensure semantic integrity-for example-by helping to make sure that a date is treated as a date rather than simply as text.

What is RDF schema

A standard for specifying consistency rules that apply to the specifications contained in an RDF.

What is realm

See security policy domain. Also, a string, passed as part of an HTTP request during basic authentication, that defines a protection space. The protected resources on a server can be partitioned into a set of protection spaces, each with its own authentication scheme or authorization database or both.

In the J2EE server authentication service, a realm is a complete database of roles, users, and groups that identify valid users of a Web application or a set of Web applications.

What is reentrant entity bean

An entity bean that can handle multiple simultaneous, interleaved, or nested invocations that will not interfere with each other.

What is reference

See entity reference.

What is registry

An infrastructure that enables the building, deployment, and discovery of Web services. It is a neutral third party that facilitates dynamic and loosely coupled business-to-business (B2B) interactions.

What is registry provider

An implementation of a business registry that conforms to a specification for XML registries (for example, ebXML or UDDI).

What is relationship field

A virtual field of an entity bean having container-managed persistence; it identifies a related entity bean.

What is remote interface

One of two interfaces for an enterprise bean. The remote interface defines the business methods callable by a client.

What is remove method

Method defined in the home interface and invoked by a client to destroy an enterprise bean.

What is render kit

A set of renderers that render output to a particular client. The JavaServer Faces implementation provides a standard HTML render kit, which is composed of renderers that can render HMTL markup.

What is renderer

A Java class that can render the output for a set of JavaServer Faces UI components.

What is request-response messaging

A method of messaging that includes blocking until a response is received.

What is resource adapter

A system-level software driver that is used by an EJB container or an application client to connect to an enterprise information system. A resource adapter typically is specific to an enterprise information system. It is available as a library and is used within the address space of the server or client using it. A resource adapter plugs in to a container. The application components deployed on the container then use the client API (exposed by the adapter) or tool-generated high-level abstractions to access the underlying enterprise information system. The resource adapter and EJB container collaborate to provide the underlying mechanisms-transactions, security, and connection pooling-for connectivity to the enterprise information system.

What is resource adapter module

A deployable unit that contains all Java interfaces, classes, and native libraries, implementing a resource adapter along with the resource adapter deployment descriptor.

What is resource manager

Provides access to a set of shared resources. A resource manager participates in transactions that are externally controlled and coordinated by a transaction manager. A resource manager typically is in a different address space or on a different machine from the clients that access it. Note: An enterprise information system is referred to as a resource manager when it is mentioned in the context of resource and transaction management.

What is resource manager connection

An object that represents a session with a resource manager.

What is resource manager connection factory

An object used for creating a resource manager connection.

What is RMI

Remote Method Invocation. A technology that allows an object running in one Java virtual machine to invoke methods on an object running in a different Java virtual machine.

What is RMI-IIOP

A version of RMI implemented to use the CORBA IIOP protocol. RMI over IIOP provides interoperability with CORBA objects implemented in any language if all the remote interfaces are originally defined as RMI interfaces.

What is role (development)

The function performed by a party in the development and deployment phases of an application developed using J2EE technology. The roles are application component provider, application assembler, deployer, J2EE product provider, EJB container provider, EJB server provider, Web container provider, Web server provider, tool provider, and system administrator.

What is role mapping

The process of associating the groups or principals (or both), recognized by the container with security roles specified in the deployment descriptor. Security roles must be mapped by the deployer before a component is installed in the server.

What is role (security)

An abstract logical grouping of users that is defined by the application assembler. When an application is deployed, the roles are mapped to security identities, such as principals or groups, in the operational environment.

In the J2EE server authentication service, a role is an abstract name for permission to access a particular set of resources. A role can be compared to a key that can open a lock. Many people might have a copy of the key; the lock doesn't care who you are, only that you have the right key.

What is rollback

The point in a transaction when all updates to any resources involved in the transaction are reversed.

What is root

The outermost element in an XML document. The element that contains all other elements.

What is SAX

Abbreviation of Simple API for XML.

What is Simple API for XML

An event-driven interface in which the parser invokes one of several methods supplied by the caller when a parsing event occurs. Events include recognizing an XML tag, finding an error, encountering a reference to an external entity, or processing a DTD specification.

What is schema

A database-inspired method for specifying constraints on XML documents using an XML-based language. Schemas address deficiencies in DTDs, such as the inability to put constraints on the kinds of data that can occur in a particular field. Because schemas are founded on XML, they are hierarchical. Thus it is easier to create an unambiguous specification, and it is possible to determine the scope over which a comment is meant to apply.

What is Secure Socket Layer (SSL)

A technology that allows Web browsers and Web servers to communicate over a secured connection.

What is security attributes

A set of properties associated with a principal. Security attributes can be associated with a principal by an authentication protocol or by a J2EE product provider or both.

What is security constraint

A declarative way to annotate the intended protection of Web content. A security constraint consists of a Web resource collection, an authorization constraint, and a user data constraint.

What is security context

An object that encapsulates the shared state information regarding security between two entities.

What is security permission

A mechanism defined by J2SE, and used by the J2EE platform to express the programming restrictions imposed on application component developers.

What is security permission set

The minimum set of security permissions that a J2EE product provider must provide for the execution of each component type.

What is security policy domain

A scope over which security policies are defined and enforced by a security administrator. A security policy domain has a collection of users (or principals), uses a well-defined authentication protocol or protocols for authenticating users (or principals), and may have groups to simplify setting of security policies.

What is security role

See role (security).

What is security technology domain

A scope over which the same security mechanism is used to enforce a security policy. Multiple security policy domains can exist within a single technology domain.

What is security view

The set of security roles defined by the application assembler.

What is server certificate

Used with the HTTPS protocol to authenticate Web applications. The certificate can be self-signed or approved by a certificate authority (CA). The HTTPS service of the Sun Java System Application Server Platform Edition 8 will not run unless a server certificate has been installed.

What is server principal

The OS principal that the server is executing as.

What is service element

A representation of the combination of one or more Connector components that share a single engine component for processing incoming requests.

What is service endpoint interface

A Java interface that declares the methods that a client can invoke on a Web service.

What is servlet

A Java program that extends the functionality of a Web server, generating dynamic content and interacting with Web applications using a request-response paradigm.

What is servlet container

A container that provides the network services over which requests and responses are sent, decodes requests, and formats responses. All servlet containers must support HTTP as a protocol for requests and responses but can also support additional request-response protocols, such as HTTPS.

What is servlet container, distributed

A servlet container that can run a Web application that is tagged as distributable and that executes across multiple Java virtual machines running on the same host or on different hosts.

What is servlet context

An object that contains a servlet's view of the Web application within which the servlet is running. Using the context, a servlet can log events, obtain URL references to resources, and set and store attributes that other servlets in the context can use.

What is servlet mapping

Defines an association between a URL pattern and a servlet. The mapping is used to map requests to servlets.

What is session

An object used by a servlet to track a user's interaction with a Web application across multiple HTTP requests. What is session bean

An enterprise bean that is created by a client and that usually exists only for the duration of a single client-server session. A session bean performs operations, such as calculations or database access, for the client. Although a session bean can be transactional, it is not recoverable should a system crash occur. Session bean objects either can be stateless or can maintain conversational state across methods and transactions. If a session bean maintains state, then the EJB container manages this state if the object must be removed from memory. However, the session bean object itself must manage its own persistent data.

What is SGML

Standard Generalized Markup Language. The parent of both HTML and XML. Although HTML shares SGML's propensity for embedding presentation information in the markup, XML is a standard that allows information content to be totally separated from the mechanisms for rendering that content.

What is SOAP

Simple Object Access Protocol. A lightweight protocol intended for exchanging structured information in a decentralized, distributed environment. It defines, using XML technologies, an extensible messaging framework containing a message construct that can be exchanged over a variety of underlying protocols.

What is SOAP with Attachments API for Java (SAAJ)

The basic package for SOAP messaging, SAAJ contains the API for creating and populating a SOAP message.

What is SQL

Structured Query Language. The standardized relational database language for defining database objects and manipulating data.

What is SQL/J

A set of standards that includes specifications for embedding SQL statements in methods in the Java programming language and specifications for calling Java static methods as SQL stored procedures and user-defined functions. An SQL checker can detect errors in static SQL statements at program development time, rather than at execution time as with a JDBC driver.

What is SSL

Secure Socket Layer. A security protocol that provides privacy over the Internet. The protocol allows client-server applications to communicate in a way that cannot be eavesdropped upon or tampered with. Servers are always authenticated, and clients are optionally authenticated.

What is stateful session bean

A session bean with a conversational state.

What is stateless session bean

A session bean with no conversational state. All instances of a stateless session bean are identical.

What is system administrator

The person responsible for configuring and administering the enterprise's computers, networks, and software systems.

What is tag

In XML documents, a piece of text that describes a unit of data or an element. The tag is distinguishable as markup, as opposed to data, because it is surrounded by angle brackets (<>). To treat such markup syntax as data, you use an entity reference or a CDATA section.

What is template

A set of formatting instructions that apply to the nodes selected by an XPath expression.

What is tool provider

An organization or software vendor that provides tools used for the development, packaging, and deployment of J2EE applications.What is topic

See publish-subscribe messaging system.

What is transaction

An atomic unit of work that modifies data. A transaction encloses one or more program statements, all of which either complete or roll back. Transactions enable multiple users to access the same data concurrently.

What is transaction attribute

A value specified in an enterprise bean's deployment descriptor that is used by the EJB container to control the transaction scope when the enterprise bean's methods are invoked. A transaction attribute can have the following values: Required, RequiresNew, Supports, NotSupported, Mandatory, or Never.

What is transaction isolation level

The degree to which the intermediate state of the data being modified by a transaction is visible to other concurrent transactions and data being modified by other transactions is visible to it.

What is transaction manager

Provides the services and management functions required to support transaction demarcation, transactional resource management, synchronization, and transaction context propagation.

What is Unicode

A standard defined by the Unicode Consortium that uses a 16-bit code page that maps digits to characters in languages around the world. Because 16 bits covers 32,768 codes, Unicode is large enough to include all the world's languages, with the exception of ideographic languages that have a different character for every concept, such as Chinese. For more information, see http://www.unicode.org/.

What is Universal Description, Discovery and Integration (UDDI) project

An industry initiative to create a platform-independent, open framework for describing services, discovering businesses, and integrating business services using the Internet, as well as a registry. It is being developed by a vendor consortium.

What is Universal Standard Products and Services Classification (UNSPSC)

A schema that classifies and identifies commodities. It is used in sell-side and buy-side catalogs and as a standardized account code in analyzing expenditure.

What is unparsed entity

A general entity that contains something other than XML. By its nature, an unparsed entity contains binary data.

What is URI

Uniform resource identifier. A globally unique identifier for an abstract or physical resource. A URL is a kind of URI that specifies the retrieval protocol (http or https for Web applications) and physical location of a resource (host name and host-relative path). A URN is another type of URI.

What is URL

Uniform resource locator. A standard for writing a textual reference to an arbitrary piece of data in the World Wide Web. A URL looks like this: protocol://host/localinfo where protocol specifies a protocol for fetching the object (such as http or ftp), host specifies the Internet name of the targeted host, and localinfo is a string (often a file name) passed to the protocol handler on the remote host.

What is URL path

The part of a URL passed by an HTTP request to invoke a servlet. A URL path consists of the context path + servlet path + path info, where Context path is the path prefix associated with a servlet context of which the servlet is a part. If this context is the default context rooted at the base of the Web server's URL namespace, the path prefix will be an empty string. Otherwise, the path prefix starts with a / character but does not end with a / character.

Servlet path is the path section that directly corresponds to the mapping that activated this request. This path starts with a / character.

Path info is the part of the request path that is not part of the context path or the servlet path.

What is URN

Uniform resource name. A unique identifier that identifies an entity but doesn't tell where it is located. A system can use a URN to look up an entity locally before trying to find it on the Web. It also allows the Web location to change, while still allowing the entity to be found.

What is user data constraint

Indicates how data between a client and a Web container should be protected. The protection can be the prevention of tampering with the data or prevention of eavesdropping on the data.

What is user (security)

An individual (or application program) identity that has been authenticated. A user can have a set of roles associated with that identity, which entitles the user to access all resources protected by those roles.

What is valid

A valid XML document, in addition to being well formed, conforms to all the constraints imposed by a DTD. It does not contain any tags that are not permitted by the DTD, and the order of the tags conforms to the DTD's specifications.

What is validating parser

A parser that ensures that an XML document is valid in addition to being well formed. See also parser.

What is value-binding expression

A JavaServer Faces EL expression that refers to a property of a backing bean. A component tag uses this expression to bind the associated component's value or the component instance to the bean property. If the component tag refers to the property via its value attribute, then the component's value is bound to the property. If the component tag refers to the property via its binding attribute then the component itself is bound to the property.

What is virtual host

Multiple hosts plus domain names mapped to a single IP address.

What is W3C

World Wide Web Consortium. The international body that governs Internet standards. Its Web site is http://www.w3.org/.

What is WAR file

Web application archive file. A JAR archive that contains a Web module.

What is warning

A SAX parser warning is generated when the document's DTD contains duplicate definitions and in similar situations that are not necessarily an error but which the document author might like to know about, because they could be. See also fatal error, error.

What is Web application

An application written for the Internet, including those built with Java technologies such as JavaServer Pages and servlets, as well as those built with non-Java technologies such as CGI and Perl.

What is Web application, distributable

A Web application that uses J2EE technology written so that it can be deployed in a Web container distributed across multiple Java virtual machines running on the same host or different hosts. The deployment descriptor for such an application uses the distributable element.

What is Web component

A component that provides services in response to requests; either a servlet or a JSP page.

What is Web container

A container that implements the Web component contract of the J2EE architecture. This contract specifies a runtime environment for Web components that includes security, concurrency, life-cycle management, transaction, deployment, and other services. A Web container provides the same services as a JSP container as well as a federated view of the J2EE platform APIs. A Web container is provided by a Web or J2EE server.

What is Web container, distributed

A Web container that can run a Web application that is tagged as distributable and that executes across multiple Java virtual machines running on the same host or on different hosts.

What is Web container provider

A vendor that supplies a Web container.

What is Web module

A deployable unit that consists of one or more Web components, other resources, and a Web application deployment descriptor contained in a hierarchy of directories and files in a standard Web application format.

What is Web resource

A static or dynamic object contained in a Web application that can be referenced by a URL.

What is Web resource collection

A list of URL patterns and HTTP methods that describe a set of Web resources to be protected.

What is Web server

Software that provides services to access the Internet, an intranet, or an extranet. A Web server hosts Web sites, provides support for HTTP and other protocols, and executes server-side programs (such as CGI scripts or servlets) that perform certain functions. In the J2EE architecture, a Web server provides services to a Web container. For example, a Web container typically relies on a Web server to provide HTTP message handling. The J2EE architecture assumes that a Web container is hosted by a Web server from the same vendor, so it does not specify the contract between these two entities. A Web server can host one or more Web containers.

What is Web server provider

A vendor that supplies a Web server.

What is Web service

An application that exists in a distributed environment, such as the Internet. A Web service accepts a request, performs its function based on the request, and returns a response. The request and the response can be part of the same operation, or they can occur separately, in which case the consumer does not need to wait for a response. Both the request and the response usually take the form of XML, a portable data-interchange format, and are delivered over a wire protocol, such as HTTP.

What is well-formed

An XML document that is syntactically correct. It does not have any angle brackets that are not part of tags, all tags have an ending tag or are themselves self-ending, and all tags are fully nested. Knowing that a document is well formed makes it possible to process it. However, a well-formed document may not be valid. To determine that, you need a validating parser and a DTD.

What is Xalan

An interpreting version of XSLT.

What is XHTML

An XML look-alike for HTML defined by one of several XHTML DTDs. To use XHTML for everything would of course defeat the purpose of XML, because the idea of XML is to identify information content, and not just to tell how to display it. You can reference it in a DTD, which allows you to say, for example, that the text in an element can contain and tags rather than being limited to plain text.

What is XLink

The part of the XLL specification that is concerned with specifying links between documents.

What is XLL

The XML Link Language specification, consisting of XLink and XPointer.

What is XML

Extensible Markup Language. A markup language that allows you to define the tags (markup) needed to identify the content, data, and text in XML documents. It differs from HTML, the markup language most often used to present information on the Internet. HTML has fixed tags that deal mainly with style or presentation. An XML document must undergo a transformation into a language with style tags under the control of a style sheet before it can be presented by a browser or other presentation mechanism. Two types of style sheets used with XML are CSS and XSL. Typically, XML is transformed into HTML for presentation. Although tags can be defined as needed in the generation of an XML document, a document type definition (DTD) can be used to define the elements allowed in a particular type of document. A document can be compared by using the rules in the DTD to determine its validity and to locate particular elements in the document. A Web services application's J2EE deployment descriptors are expressed in XML with schemas defining allowed elements. Programs for processing XML documents use SAX or DOM APIs.

What is XML registry

See registry.

What is XML Schema

The W3C specification for defining the structure, content, and semantics of XML documents.

What is XPath

An addressing mechanism for identifying the parts of an XML document.

What is XPointer

The part of the XLL specification that is concerned with identifying sections of documents so that they can be referenced in links or included in other documents.

What is XSL

Extensible Stylesheet Language. A standard that lets you do the following:

Specify an addressing mechanism, so that you can identify the parts of an XML document that a transformation applies to (XPath).

Specify tag conversions, so that you can convert XML data into different formats (XSLT).

Specify display characteristics, such page sizes, margins, and font heights and widths, as well as the flow objects on each page. Information fills in one area of a page and then automatically flows to the next object when that area fills up. That allows you to wrap text around pictures, for example, or to continue a newsletter article on a different page (XSL-FO).

What is XSL-FO

A subcomponent of XSL used for describing font sizes, page layouts, and how information flows from one page to another.

What is XSLT

XSL Transformations. An XML document that controls the transformation of an XML document into another XML document or HTML. The target document often has presentation-related tags dictating how it will be rendered by a browser or other presentation mechanism. XSLT was formerly a part of XSL, which also included a tag language of style flow objects.

What is XSLTC

A compiling version of XSLT