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.

Java Interview Questions

1: OOPS and CORE JAVA
· What is JVM (Java Virtual Machine)?
· What is JIT (Just- in-Time) Compilation?
· What is Object Oriented Programming?
· What’s a Class?
· What’s an Object?
· What’s the relation between Classes and Objects?
· What are different properties provided by Object-oriented systems?
· How do you implement inheritance in Java?
· How can we implement polymorphism in Java?
· What is an Abstract class?
· What are Abstract methods?
· What’s the difference between “Abstract” classes and “Interfaces”?
· What’s difference between Static and Non-Static fields of a class?
· What are inner classes and what’s the practical implementation of inner classes?
· What are packages?
· What is a constructor in class?
· Can constructors be parameterized?
· What is the use if “instance of” keyword?
· What are Native methods in Java?
· How do refer to a current instance of object?
· Explain in depth Garbage collector?
· How does the garbage collector determine that the object has to be marked for
deletion?
· Can you explain “finalize ()” method?
· How can we force the garbage collector to run?
· What’s the main difference between “Switch” and “If” comparison?
· What’s the use of JAVAP tool?
· What are applets?
· In which package is, the applet class located?
· What are native interfaces in Java?
· What are Class loaders?
· What is Bootstrap, Extension and System Class loader?
· Can you explain the flow between bootstrap, extension and system class loader?
· Can you explain how can you practically do dynamic loading?
· What is Reflection API in Java?
· What’s the difference between static and dynamic class loading?
· How can you copy one array in to a different array?
· Can you explain the core collection interfaces?
· Can you explain in brief the collection classes which implement the collection
interfaces?
· What’s the difference between standard JAVA array and Array List class?
· What’s the use of “ensure Capacity” in Array List class?
· How can we obtain an array from an Array List class?
· What is “Linked List” class for?
· Can you explain Hash Set class in collections?
· What is Linked Hash Set class?
· What is a Tree Set class?
· What’s the use of Comparator Interface?
· How can we access elements of a collection?
· What is Map and SortedMap Interface?
· Have you used any collection algorithm?
· Why do we use collections when we had traditional ways for collection?
· Can you name the legacy classes and interface for collections?
· What is Enumeration Interface?
· What’s the main difference between Array List / Hash Map and Vector / Hash
table?
· Are String object Immutable, Can you explain the concept?
· What is a String Buffer class and how does it differs from String class?
· What is the difference between String Builder and String Buffer class?
· What is Pass by Value and Pass by reference? How does JAVA handle the same?
· What are access modifiers?
· What is Assertion?
· Can you explain the fundamentals of deep and shallow Cloning?
· How do we implement shallow cloning?
· How do we implement deep cloning?
· What’s the impact of private constructor?
· What are the situations you will need a constructor to be private?
· Can you explain final modifier?
· What are static Initializes?
· If we have multiple static initialize blocks how are the sequence handled?
· Define casting? What are the different types of Casting?
· Can you explain Widening conversion and Narrowing conversion?
· Can we assign parent object to child objects?
· Define exceptions?
· Can you explain in short how JAVA exception handling works?
· Can you explain different exception types?
· Can you explain checked and unchecked exceptions?
· Can we create our own exception class?
· What are chained exceptions?
· What is serialization?
· How do we implement serialization actually?
· What’s the use of Externalizable Interface?
· What is JAVA doc utility?
2: Threading
· What’s difference between thread and process?
· What is thread safety and synchronization?
· What is semaphore?
· What are monitors?
· What’s the importance of synchronized blocks?
· How do we create threads?
· What’s the difference in using run able and extends in threads?
· Can you explain Thread. Sleep?
· How to stop a thread?
· What is wait () and notify ()?
· Can you explain how Scheduling and Priority works in threads?
· Can you explain Yielding in threading?
· What are daemon threads?
· How do we implement single threaded model in servlets?
3: JDBC
· How does JAVA interact with databases?
· Can we interact with non-relational sources using JDBC?
· Can you explain in depth the different sections in JDBC?
· Can you explain in short how you go about using JDBC API in code?
· How do you handle SQL exceptions?
Twist: - (A) Can you explain “SQL Exception” class in detail?
Twist: - (A) what is SQL State in SQL Exceptions?
· If there is more than one exception in SQL Exception” class how to go about
displaying it?
· Explain Type1, Type2, Type3, and Type4 drivers in JDBC?
· What are the advantages and disadvantages of using JDBC-ODBC bridge driver?
· What are the advantages and disadvantages of using Native-API/ Partially Java
Driver?
· What are the advantages and disadvantages of using Net-Protocol/ All-Java
driver?
· What are the advantages and disadvantages of using Native-protocol/ All-Java
driver?
· Advantages of using JDBC-ODBC bridge driver:-
· Disadvantages of using JDBC-ODBC bridge driver:-
· Advantages of using Native-API/ Partially Java Driver:-
· Dis-advantages of using Native-API/ Partially Java Driver:-
· Advantages of using Net-Protocol/ All-Java driver:-
· Disadvantages of using Net-Protocol/ All- Java driver:-
· Advantages of using Native-protocol/ All-Java driver:-
· Disadvantages of using Native-protocol/ All-Java driver:-
· Define meta-data?
· What is Database Metadata?
· Can you explain “Connection Factory” class?
· I want to display tables of a database how do I do it?
· Define “Result Set Meta Data”?
· What is the difference between “Result Set” and “Row Set”?
· Can “Result Set” objects be serialized?
· Explain “Result Set”, “Row Set”, “Cached Row set”, “JdbcRowset” and “Web
Row Set”?
· What are the different types of result set?
· Explain the concept of “Prepared Statement “statement interface?
· What’s the difference between “Statement” and “Prepared Statement”?
· How can we call stored procedure using JDBC?
· Can you explain “Callable Statement” interface in detail?
· How do you get a result set object from stored procedure?
· (A) How can we do batch updates using “Callable Statement” Interface?
· Define transactions?
· What is ACID in transaction?
· What are the four essential properties of a transaction?
· Explain concurrency and locking?
· What are different types of locks?
· What are the different types of levels of resource on which locks can be placed?
· Define lock escalation?
· What is Table level and Row level locking?
· What are the problems that can occur if you do not implement locking properly?
· What are different transaction levels?
· Twist: - what are different types of locks?
· What is difference between optimistic and pessimistic locking?
· What are deadlocks?
· How can we set transaction level through JDBC API?
· Can you explain transaction control in JDBC?
· What are Save points in a transaction?
4: Servlets and JSP
· What are Servlets?
· What are advantages of servlets over CGI?
· Can you explain Servlet life cycle?
· What are the two important API’s in for Servlets?
· Can you explain in detail “javax.servlet” package?
· What’s the use of Servlet Context?
· How do we define an application level scope for servlet?
· What's the difference between Generic Servlet and Http Servlet?
· Can you explain in detail javax.servlet.http package?
· What’s the architecture of a Servlet package?
· Why is HTTP protocol called as a stateless protocol?
· What are the different ways we can maintain state between requests?
· What is URL rewriting?
· What are cookies?
· What are sessions in Servlets?
· What the difference is between get Session (true) and get Session (false)?
· What’s the difference between “do Post” and “do get” methods?
· Which are the different ways you can communicate between servlets?
· What is functionality of “Request Dispatcher” object?
· How do we share data using “get Servlet Context ()”?
· Explain the concept of SSI?
· What are filters in JAVA?
· Can you explain in short how do you go about implementing filters using Apache
Tomcat?
· Twist: - Explain step by step of how to implement filters?
· What’s the difference between Authentication and authorization?
· Explain in brief the directory structure of a web application?
· Can you explain JSP page life cycle?
· What is EL?
· How does EL search for an attribute?
· What are the implicit EL objects in JSP?
· How can we disable EL?
· What is JSTL?
· Can you explain in short what the different types of JSTL tags are?
· (I) How can we use beans in JSP?
· What is the use of ?
· What is tag for?
· What are JSP directives?
· What are Page directives?
· What are including directives?
· Can you explain taglib directives?
· How does JSP engines instantiate tag handler classes’ instances?
· What’s the difference between JavaBeans and taglib directives?
· What are the different scopes an object can have in a JSP page?
· What are different implicit objects of JSP?
· What are different Authentication Options available in servlets?
· Can you explain how do we practically implement security on a resource?
· How do we practically implement form based authentication?
· How do we authenticate using JDBC?
· Can you explain JDBCRealm?
· Can you explain how do you configure JNDIRealm?
· How did you implement caching in JSP?
· What is the difference between Servletcontext and ServletConfig?
· How do we prevent browser from caching output of my JSP pages?
· Can we explicitly destroy a servlet object?
5: EJB
· What is EJB?
· What are the different kind of Ebb’s?
· You are designing architecture for a project how do you decide whether you
should use session, entity or message driven bean?
· Can you explain “EJBHome” and “EJBObject” in EJB?
· Can client directly create object of session or entity beans?
· Can you explain the concept of local interfaces?
· What are the limitations of using Local object?
· Which application server have you used for EJB?
· Can you explain step by step practically developing and deploying EJB
component?
· What is Passivation and Activation in EJB?
· Can beans who are involved in transaction have “Passivation” process?
· How does the server decide which beans to passivity and activate?
· In what format is the conversational data written to the disk?
· Can you explain in brief Life cycle for Stateless and Stateful beans?
6: Struts
· (I)What’s MVC pattern?
· (B) Define struts?
· (A) Can you explain the directory structure for a struts folder in brief?
· (I) Can you give an overview of how a struts application flows?
· Twist: - What are action and action form classes in Struts?
7: XML and Web Services
· What is XML?
· What is the version information in XML?
· What is ROOT element in XML?
· If XML does not have closing tag will it work?
· Is XML case sensitive?
· What is the difference between XML and HTML?
· Is XML meant to replace HTML?
· Can you explain why your project needed XML?
· What is DTD (Document Type definition)?
· What is well formed XML?
· What is a valid XML?
· What is CDATA section in XML?
· What is CSS?
· What is XSL?
· What is element and attributes in XML?
· What are the standard ways of parsing XML document?
· In What scenarios will you use a DOM parser and SAX parser?
· What is XSLT?
· Define XPATH?
· What is the concept of XPOINTER?
· What is a Web Service?
· What is DISCO?
· What is SOAP?
· What is WSDL?
· Can you explain UDDI?
· Can you explain JAXP?
· What is a XML registry?
· What is JAXR?
· What is JAXM?
· Can you explain JAX-RPC?
· How do you practically implement Web Services?
· How do we consume a web service?
· Are web services Stateful?
8: Internationalization
· Can you explain i18n and l10n?
· Can you explain internationalization and localization?
· What is Locale?
· How do we display numbers, currency and Dates according to proper Locale
format?
· what are resource bundles?
· How do we load a resource bundle file?
· How can we do inheritance in resource bundles?
9: JNI
· What is Native Interface in JAVA?
· Can you say in brief steps required to implement Native interfaces in Java?
· Can JNI be used for VB6, C# or VB.NET directly?
· What are JNI functions and pointers?
· How does the garbage collector know JNI objects are no more used?
· Twist: - What are the different types of references JNI supports?
· Twist: - How to do you delete global objects?
· How does the native language C or C++ understand data types in JAVA?
· Can you explain exception handling in JNI?
· What are limitations for “JNIEnv” pointer in multi- threading scenarios?
· What are the advantages and disadvantages of using “JNI”?
10: Architecture
· What are design patterns?
· Can you list down all patterns and their classification?
· What is the difference between Factory and Abstract Factory Patterns?
· What is MVC pattern?
· How can we implement singleton pattern in JAVA?
· How do you implement prototype pattern in JAVA?
· Can you give a practical implementation of FAÇADE patterns?
· How can we implement observer pattern in JAVA?
· What is three tier architecture?
· What is Service Oriented architecture?
· What is aspect oriented programming?
· How can you implement AOP practically in JAVA?
· What is Inversion of control?
· What is OR mapping?
11: UML
· What is UML?
· How many types of diagrams are there in UML?
· What are advantages of using UML?
· What is the sequence of UML diagrams in project?
· Give a small brief explanation of all Elements in activity diagrams?
· Explain Different elements of a collaboration diagram?
· Explain Component diagrams?
· Describe the various components in sequence diagrams?
· What are the elements in State Chart diagrams?
· Describe different elements in Static Chart diagrams?
· Explain the different elements of a Use Case?
12: Project Management
· What is project management?
· Is spending in IT projects constant through out the project?
· Who is a stakeholder?
· Can you explain project life cycle?
· Are risk constant through out the project?
· Can you explain different software development life cycles?
· What is triple constraint triangle in project management?
· What is a project baseline?
· What is effort variance?
· How is normally a project management plan document organized?
· (I)How do you estimate a project?
· What is CAR (Causal Analysis and Resolution)?
· What is DAR (Decision Analysis and Resolution)?
· What is a fish bone diagram?
· What is pare to principle?
· How do you handle change request?
· What is internal change request?
· What is difference between SITP and UTP in testing?
· What is the software you have used for project management?
· What are the metrics followed in project management?
· You have people in your team who do not meet there deadlines or do not perform
what are the actions you will take?
· What is black box testing and White box testing?
· What’s the difference between Unit testing, Assembly testing and Regression
testing?
· What is V model in testing?
· How do you start a project?
· How did you do resource allocations?
· How will you do code reviews?
· What is CMMI?
· What are the five levels in CMMI?
· What is continuous and staged representation?
· Can you explain the process areas?
· What is SIX sigma?
· What is DMAIC and DMADV?
· What are the various roles in Six Sigma implementation?
· What are function points?
· What are the different types of elementary process in FPA?
· What are the different elements in Functions points?
· Can you explain in GSC and VAF in function points?
· What are unadjusted function points and how is it calculated?
· Can you explain steps in function points?
· What is the FP per day in your current company?
· Do you know Use Case points?
· What is COCOMO I, COCOMOII and COCOMOIII?
· What is SMC approach of estimation?
· How do you estimate maintenance project and change requests?
13: Database
· What is database or database management systems (DBMS)?
· What is SQL?
· What’s difference between DBMS and RDBMS?
· What are CODD rules?
· What are E-R diagrams?
· How many types of relationship exist in database designing? What is
normalization? What are different type of normalization?
· What is denormalization?
· Can you explain Fourth Normal Form?
· Can you explain Fifth Normal Form?
· What’s the difference between Fourth and Fifth normal form?
· Have you heard about sixth normal form?
· What are DML and DDL statements?
· How do we select distinct values from a table?
· What is like operator for and what are wild cards?
· Can you explain Insert, Update and Delete query?
· What is order by clause?
· What is the SQL In clause?
· Can you explain the between clause?
· I have an employee salary table how do we find the second highest from it?
· What are different types of joins in SQL?
· What is “CROSS JOIN”?
· You want to select the first record in a given set of rows?
· What is the default “SORT” order for a SQL?
· What is a self-join?
· What’s the difference between DELETE and TRUNCATE?
· .What are Wildcard operators?
· Twist: - What is like clause in SQL?
· What’s the difference between “UNION” and “UNION ALL”?
· What are cursors and what are the situations you will use them?
· What are the steps to create a cursor?
· What is “Group by” clause?
· What is the difference between “HAVING” and “WHERE” clause?
· What is a Sub-Query?
· What are Aggregate and Scalar Functions?
· Can you explain the SELECT INTO Statement?
· What is a View?
· What is “Correlated Sub queries”?
· What is SQl injection?
· What is “Data Warehousing”?
· What are Data Marts?
· What are Fact tables and Dimension Tables?
· Twist: - What is Dimensional Modeling?
· Twist: - What is Star Schema Design?
· What is Snow Flake Schema design in database?
· Twist: - What’s the difference between Star and Snow flake schema?
· What is ETL process in Data warehousing?
· Twist: - What are the different stages in “Data warehousing”?
· What is “Data mining”?
· Compare “Data mining” and “Data Warehousing”?
· What are indexes?
· What are B-Trees?
· I have a table which has lot of inserts, is it a good database design to create
indexes on that table?
· Twist: - Insert’s are slower on tables which have indexes, justify it?
· Twist: - Why do page splitting happen?
· What are “Table Scan’s” and “Index Scan’s”?
· What are the two types of indexes and explain them in detail?
· Twist: - What’s the difference between clustered and non-clustered indexes?

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

1. What is a transient variable?
A transient variable is a variable that may not be serialized.

2. Which containers use a border Layout as their default layout?
The window, Frame and Dialog classes use a border layout as their default layout.

3. Why do threads block on I/O?
Threads block on I/O (that is enters the waiting state) so that other threads may execute while the I/O Operation is performed.

4. How are Observer and Observable used?
Objects that subclass the Observable class maintain a list of observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects.

5. What is synchronization and why is it important?
With respect to multithreading, synchronization is the capability to control the access of multiple threads to shared resources. Without synchronization, it is possible for one thread to modify a shared object while another thread is in the process of using or updating that object's value. This often leads to significant errors.

6. Can a lock be acquired on a class?
Yes, a lock can be acquired on a class. This lock is acquired on the class's Class object.

7. What's new with the stop(), suspend() and resume() methods in JDK 1.2?
The stop(), suspend() and resume() methods have been deprecated in JDK 1.2.

8. Is null a keyword?
The null value is not a keyword.

9. What is the preferred size of a component?
The preferred size of a component is the minimum component size that will allow the component to display normally.

10. What method is used to specify a container's layout?
The setLayout() method is used to specify a container's layout.

11. Which containers use a FlowLayout as their default layout?
The Panel and Applet classes use the FlowLayout as their default layout.

12. What state does a thread enter when it terminates its processing?
When a thread terminates its processing, it enters the dead state.

13. What is the Collections API?
The Collections API is a set of classes and interfaces that support operations on collections of objects.

14. which characters may be used as the second character of an identifier, but not as the first character of an identifier?
The digits 0 through 9 may not be used as the first character of an identifier but they may be used after the first character of an identifier.

15. What is the List interface?
The List interface provides support for ordered collections of objects.

16. How does Java handle integer overflows and underflows?
It uses those low order bytes of the result that can fit into the size of the type allowed by the operation.

17. What is the Vector class?
The Vector class provides the capability to implement a growable array of objects

18. What modifiers may be used with an inner class that is a member of an outer class?
A (non-local) inner class may be declared as public, protected, private, static, final, or abstract.

19. What is an Iterator interface?
The Iterator interface is used to step through the elements of a Collection.

20. What is the difference between the >> and >>> operators?
The >> operator carries the sign bit when shifting right. The >>> zero-fills bits that have been shifted out.

21. Which method of the Component class is used to set the position and size of a component?
setBounds()

22. How many bits are used to represent Unicode, ASCII, UTF-16, and UTF-8 characters?
Unicode requires 16 bits and ASCII require 7 bits. Although the ASCII character set uses only 7 bits, it is usually represented as 8 bits. UTF-8 represents characters using 8, 16, and 18 bit patterns. UTF-16 uses 16-bit and larger bit patterns.

23 What is the difference between yielding and sleeping?
When a task invokes its yield() method, it returns to the ready state. When a task invokes its sleep() method, it returns to the waiting state.

24. Which java.util classes and interfaces support event handling?
The EventObject class and the EventListener interface support event processing.

25. Is sizeof a keyword?
The sizeof operator is not a keyword.

26. What are wrapper classes?
Wrapper classes are classes that allow primitive types to be accessed as objects.

27. Does garbage collection guarantee that a program will not run out of memory?
Garbage collection does not guarantee that a program will not run out of memory. It is possible for programs to use up memory resources faster than they are garbage collected. It is also possible for programs to create objects that are not subject to garbage collection.

28. What restrictions are placed on the location of a package statement within a source code file?
A package statement must appear as the first line in a source code file (excluding blank lines and comments).

29. Can an object's finalize() method be invoked while it is reachable?
An object's finalize() method cannot be invoked by the garbage collector while the object is still reachable. However, an object's finalize() method may be invoked by other objects.

30. What is the immediate superclass of the Applet class?
Panel

31. What is the difference between preemptive scheduling and time slicing?
Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. Under time slicing, a task executes for a predefined slice of time and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors.

32. Name three Component subclasses that support painting.
The Canvas, Frame, Panel, and Applet classes support painting.

33. What value does readLine() return when it has reached the end of a file?
The readLine() method returns null when it has reached the end of a file.

34. What is the immediate superclass of the Dialog class?
Window.

35. What is clipping?
Clipping is the process of confining paint operations to a limited area or shape.

36. What is a native method?
A native method is a method that is implemented in a language other than Java.

37. Can a for statement loop indefinitely?
Yes, a for statement can loop indefinitely. For example, consider the following:
for(;;) ;

38. What are order of precedence and associativity, and how are they used?
Order of precedence determines the order in which operators are evaluated in expressions. Associatity determines whether an expression is evaluated left-to-right or right-to-left

39. When a thread blocks on I/O, what state does it enter?
A thread enters the waiting state when it blocks on I/O.

40. To what value is a variable of the String type automatically initialized?
The default value of a String type is null.

41. What is the catch or declare rule for method declarations?
If a checked exception may be thrown within the body of a method, the method must either catch the exception or declare it in its throws clause.

42. What is the difference between a MenuItem and a CheckboxMenuItem?
The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.

43. What is a task's priority and how is it used in scheduling?
A task's priority is an integer value that identifies the relative order in which it should be executed with respect to other tasks. The scheduler attempts to schedule higher priority tasks before lower priority tasks.

44. What class is the top of the AWT event hierarchy?
The java.awt.AWTEvent class is the highest-level class in the AWT event-class hierarchy.

45. When a thread is created and started, what is its initial state?
A thread is in the ready state after it has been created and started.

46. Can an anonymous class be declared as implementing an interface and extending a class?
An anonymous class may implement an interface or extend a superclass, but may not be declared to do both.

47. What is the range of the short type?
The range of the short type is -(2^15) to 2^15 - 1.

48. What is the range of the char type?
The range of the char type is 0 to 2^16 - 1.

49. In which package are most of the AWT events that support the event-delegation model defined?
Most of the AWT-related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package.

50. What is the immediate superclass of Menu?
MenuItem

51. What is the purpose of finalization?
The purpose of finalization is to give an unreachable object the opportunity to perform any cleanup processing before the object is garbage collected.

52. Which class is the immediate superclass of the MenuComponent class.
Object

53. What invokes a thread's run() method?
After a thread is started, via its start() method or that of the Thread class, the JVM invokes the thread's run() method when the thread is initially executed.

54. What is the difference between the Boolean & operator and the && operator?
If an expression involving the Boolean & operator is evaluated, both operands are evaluated. Then the & operator is applied to the operand. When an expression involving the && operator is evaluated, the first operand is evaluated. If the first operand returns a value of true then the second operand is evaluated. The && operator is then applied to the first and second operands. If the first operand evaluates to false, the evaluation of the second operand is skipped.

55. Name three subclasses of the Component class.
Box.Filler, Button, Canvas, Checkbox, Choice, Container, Label, List, Scrollbar, or TextComponent

56. What is the GregorianCalendar class?
The GregorianCalendar provides support for traditional Western calendars.

57. Which Container method is used to cause a container to be laid out and redisplayed?
validate()

58. What is the purpose of the Runtime class?
The purpose of the Runtime class is to provide access to the Java runtime system.

59. How many times may an object's finalize() method be invoked by the
garbage collector?
An object's finalize() method may only be invoked once by the garbage collector.

60. What is the purpose of the finally clause of a try-catch-finally statement?
The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown or caught.

61. What is the argument type of a program's main() method?
A program's main() method takes an argument of the String[] type.

62. Which Java operator is right associative?
The = operator is right associative.

63. What is the Locale class?
The Locale class is used to tailor program output to the conventions of a particular geographic, political, or cultural region.64. Can a double value be cast to a byte?
Yes, a double value can be cast to a byte.

65. What is the difference between a break statement and a continue statement?
A break statement results in the termination of the statement to which it applies (switch, for, do, or while). A continue statement is used to end the current loop iteration and return control to the loop statement.

66. What must a class do to implement an interface?
It must provide all of the methods in the interface and identify the interface in its implements clause.

67. What method is invoked to cause an object to begin executing as a separate thread?
The start() method of the Thread class is invoked to cause an object to begin executing as a separate thread.

68. Name two subclasses of the TextComponent class.
TextField and TextArea

69. What is the advantage of the event-delegation model over the earlier event-inheritance model?
The event-delegation model has two advantages over the event-inheritance model. First, it enables event handling to be handled by objects other than the ones that generate the events (or their containers). This allows a clean separation between a component's design and its use. The other advantage of the event-delegation model is that it performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event-inheritance
model.

70. Which containers may have a MenuBar?
Frame

71. How are commas used in the initialization and iteration parts of a for statement?
Commas are used to separate multiple statements within the initialization and iteration parts of a for statement.

72. What is the purpose of the wait(), notify(), and notifyAll() methods?
The wait(),notify(), and notifyAll() methods are used to provide an efficient way for threads to wait for a shared resource. When a thread executes an object's wait() method, it enters the waiting state. It only enters the ready state after another thread invokes the object's notify() or notifyAll() methods.

73. What is an abstract method?
An abstract method is a method whose implementation is deferred to a subclass.

74. How are Java source code files named?
A Java source code file takes the name of a public class or interface that is defined within the file. A source code file may contain at most one public class or interface. If a public class or interface is defined within a source code file, then the source code file must take the name of the public class or interface. If no public class or interface is defined within a source code file, then the file must take on a name that is different than its classes and interfaces. Source code files use the .java extension.

75. What is the relationship between the Canvas class and the Graphics class?
A Canvas object provides access to a Graphics object via its paint() method.

76. What are the high-level thread states?
The high-level thread states are ready, running, waiting, and dead.

77. What value does read() return when it has reached the end of a file?
The read() method returns -1 when it has reached the end of a file.

78. Can a Byte object be cast to a double value?
No, an object cannot be cast to a primitive value.

79. What is the difference between a static and a non-static inner class?
A non-static inner class may have object instances that are associated with instances of the class's outer class. A static inner class does not have any object instances.

80. What is the difference between the String and StringBuffer classes?
String objects are constants. StringBuffer objects are not.

81. If a variable is declared as private, where may the variable be accessed?
A private variable may only be accessed within the class in which it is declared.

82. What is an object's lock and which objects have locks?
An object's lock is a mechanism that is used by multiple threads to obtain synchronized access to the object. A thread may execute a synchronized method of an object only after it has acquired the object's lock. All objects and classes have locks. A class's lock is acquired on the class's Class object.

83. What is the Dictionary class?
The Dictionary class provides the capability to store key-value pairs.

84. How are the elements of a BorderLayout organized?
The elements of a BorderLayout are organized at the borders (North, South, East, and West) and the center of a container.

85. What is the % operator?
It is referred to as the modulo or remainder operator. It returns the remainder of dividing the first operand by the second operand.

86. When can an object reference be cast to an interface reference?
An object reference be cast to an interface reference when the object implements the referenced interface.

87. What is the difference between a Window and a Frame?
The Frame class extends Window to define a main application window that can have a menu bar.

88. Which class is extended by all other classes?
The Object class is extended by all other classes.

89. Can an object be garbage collected while it is still reachable?
A reachable object cannot be garbage collected. Only unreachable objects may be garbage collected..

90. Is the ternary operator written x : y ? z or x ? y : z ?
It is written x ? y : z.

91. What is the difference between the Font and FontMetrics classes?
The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object.

92. How is rounding performed under integer division?
The fractional part of the result is truncated. This is known as rounding toward zero.

93. What happens when a thread cannot acquire a lock on an object?
If a thread attempts to execute a synchronized method or synchronized statement and is unable to acquire an object's lock, it enters the waiting state until the lock becomes available.

94. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy?
The Reader/Writer class hierarchy is character-oriented, and the InputStream/OutputStream class hierarchy is byte-oriented.

95. What classes of exceptions may be caught by a catch clause?
A catch clause can catch any exception that may be assigned to the Throwable type. This includes the Error and Exception types.

96. If a class is declared without any access modifiers, where may the class be accessed?
A class that is declared without any access modifiers is said to have package access. This means that the class can only be accessed by other classes and interfaces that are defined within the same package.

97. What is the SimpleTimeZone class?
The SimpleTimeZone class provides support for a Gregorian calendar.

98. What is the Map interface?
The Map interface replaces the JDK 1.1 Dictionary class and is used associate keys with values.99. Does a class inherit the constructors of its superclass?
A class does not inherit constructors from any of its super classes.

100. For which statements does it make sense to use a label?
The only statements for which it makes sense to use a label are those statements that can enclose a break or continue statement.

101. What is the purpose of the System class?
The purpose of the System class is to provide access to system resources.

102. Which TextComponent method is used to set a TextComponent to the read-only state?
setEditable()

103. How are the elements of a CardLayout organized?
The elements of a CardLayout are stacked, one on top of the other, like a deck of cards.

104. Is &&= a valid Java operator?
No, it is not.

105. Name the eight primitive Java types.
The eight primitive types are byte, char, short, int, long, float, double, and boolean.

106. Which class should you use to obtain design information about an object?
The Class class is used to obtain information about an object's design.

107. What is the relationship between clipping and repainting?
When a window is repainted by the AWT painting thread, it sets the clipping regions to the area of the window that requires repainting.

108. Is "abc" a primitive value?
The String literal "abc" is not a primitive value. It is a String object.

109. What is the relationship between an event-listener interface and an event-adapter class?
An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a default implementation of an event-listener interface.

110. What restrictions are placed on the values of each case of a switch statement?
During compilation, the values of each case of a switch statement must evaluate to a value that can be promoted to an int value.

111. What modifiers may be used with an interface declaration?
An interface may be declared as public or abstract.

112. Is a class a subclass of itself?
A class is a subclass of itself.

113. What is the highest-level event class of the event-delegation model?
The java.util.EventObject class is the highest-level class in the event-delegation class hierarchy.

114. What event results from the clicking of a button?
The ActionEvent event is generated as the result of the clicking of a button.

115. How can a GUI component handle its own events?
A component can handle its own events by implementing the required event-listener interface and adding itself as its own event listener.

116. What is the difference between a while statement and a do statement?
A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once.

117. How are the elements of a GridBagLayout organized?
The elements of a GridBagLayout are organized according to a grid. However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.

118. What advantage do Java's layout managers provide over traditional windowing systems?
Java uses layout managers to lay out components in a consistent manner across all windowing platforms. Since Java's layout managers aren't tied to absolute sizing and positioning, they are able to accommodate platform-specific differences among windowing systems.

119. What is the Collection interface?
The Collection interface provides support for the implementation of a mathematical bag - an unordered collection of objects that may contain duplicates.

120. What modifiers can be used with a local inner class?
A local inner class may be final or abstract.

121. What is the difference between static and non-static variables?
A static variable is associated with the class as a whole rather than with specific instances of a class. Non-static variables take on unique values with each object instance.

122. What is the difference between the paint() and repaint() methods?
The paint() method supports painting via a Graphics object. The repaint() method is used to cause paint() to be invoked by the AWT painting thread.

123. What is the purpose of the File class?
The File class is used to create objects that provide access to the files and directories of a local file system.

124. Can an exception be rethrown?
Yes, an exception can be rethrown.

125. Which Math method is used to calculate the absolute value of a number?
The abs() method is used to calculate absolute values.

126. How does multithreading take place on a computer with a single CPU?
The operating system's task scheduler allocates execution time to multiple tasks. By quickly switching between executing tasks, it creates the impression that tasks execute sequentially.

127. When does the compiler supply a default constructor for a class?
The compiler supplies a default constructor for a class if no other constructors are provided.

128. When is the finally clause of a try-catch-finally statement executed?
The finally clause of the try-catch-finally statement is always executed unless the thread of execution terminates or an exception occurs within the execution of the finally clause.

129. Which class is the immediate superclass of the Container class?
Component

130. If a method is declared as protected, where may the method be accessed?
A protected method may only be accessed by classes or interfaces of the same package or by subclasses of the class in which it is declared.

131. How can the Checkbox class be used to create a radio button?
By associating Checkbox objects with a CheckboxGroup.

132. Which non-Unicode letter characters may be used as the first character of an identifier?
The non-Unicode letter characters $ and _ may appear as the first character of an identifier

133. What restrictions are placed on method overloading?
Two methods may not have the same name and argument list but different return types.

134. What happens when you invoke a thread's interrupt method while it is sleeping or waiting?
When a task's interrupt() method is executed, the task enters the ready state. The next time the task enters the running state, an InterruptedException is thrown.

135. What is casting?
There are two types of casting, casting between primitive numeric types and casting between object references. Casting between numeric types is used to convert larger values, such as double values, to smaller values, such as byte values. Casting between object references is used to refer to an object by a compatible class, interface, or array type reference.

136. What is the return type of a program's main() method?
A program's main() method has a void return type.

137. Name four Container classes.
Window, Frame, Dialog, FileDialog, Panel, Applet, or ScrollPane

138. What is the difference between a Choice and a List?
A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items.

139. What class of exceptions are generated by the Java run-time system?
The Java runtime system generates RuntimeException and Error exceptions.

140. What class allows you to read objects directly from a stream?
The ObjectInputStream class supports the reading of objects from input streams.

141. What is the difference between a field variable and a local variable?
A field variable is a variable that is declared as a member of a class. A local variable is a variable that is declared local to a method.

142. Under what conditions is an object's finalize() method invoked by the garbage collector?
The garbage collector invokes an object's finalize() method when it detects that the object has become unreachable.

143. How are this () and super () used with constructors?
this() is used to invoke a constructor of the same class. super() is used to invoke a superclass constructor.

144. What is the relationship between a method's throws clause and the exceptions that can be thrown during the method's execution?
A method's throws clause must declare any checked exceptions that are not caught within the body of the method.

145. What is the difference between the JDK 1.02 event model and the event-delegation model introduced with JDK 1.1?
The JDK 1.02 event model uses an event inheritance or bubbling approach. In this model, components are required to handle their own events. If they do not handle a particular event, the event is inherited by (or bubbled up to) the component's container. The container then either handles the event or it is bubbled up to its container and so on, until the highest-level container has been tried.
In the event-delegation model, specific objects are designated as event handlers for GUI components. These objects implement event-listener interfaces. The event-delegation model is more efficient than the event-inheritance model because it eliminates the processing required to support the bubbling of unhandled events.

146. How is it possible for two String objects with identical values not to be equal under the == operator?
The == operator compares two objects to determine if they are the same object in memory. It is possible for two String objects to have the same value, but located indifferent areas of memory.

147. Why are the methods of the Math class static?
So they can be invoked as if they are a mathematical code library.

148. What Checkbox method allows you to tell if a Checkbox is checked?
getState()

149. What state is a thread in when it is executing?
An executing thread is in the running state.

150. What are the legal operands of the instanceof operator?
The left operand is an object reference or null value and the right operand is a class, interface, or array type.

151. How are the elements of a GridLayout organized?
The elements of a GridBad layout are of equal size and are laid out using the squares of a grid.

152. What an I/O filter?
An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.

153. If an object is garbage collected, can it become reachable again?
Once an object is garbage collected, it ceases to exist. It can no longer become reachable again.

154. What is the Set interface?
The Set interface provides methods for accessing the elements of a finite mathematical set. Sets do not allow duplicate elements.

155. What classes of exceptions may be thrown by a throw statement?
A throw statement may throw any expression that may be assigned to the Throwable type.

156. What are E and PI?
E is the base of the natural logarithm and PI is mathematical value pi.

157. Are true and false keywords?
The values true and false are not keywords.

158. What is a void return type?
A void return type indicates that a method does not return a value.

159. What is the purpose of the enableEvents() method?
The enableEvents() method is used to enable an event for a particular object. Normally, an event is enabled when a listener is added to an object for a particular event. The enableEvents() method is used by objects that handle events by overriding their event-dispatch methods.

160. What is the difference between the File and RandomAccessFile classes?
The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file.

161. What happens when you add a double value to a String?
The result is a String object.162. What is your platform's default character encoding?
If you are running Java on English Windows platforms, it is probably Cp1252. If you are running Java on English Solaris platforms, it is most likely 8859_1..

163. Which package is always imported by default?
The java.lang package is always imported by default.

164. What interface must an object implement before it can be written to a stream as an object?
An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.

165. How are this and super used?
this is used to refer to the current object instance. super is used to refer to the variables and methods of the superclass of the current object instance.

166. What is the purpose of garbage collection?
The purpose of garbage collection is to identify and discard objects that are no longer needed by a program so that their resources may be reclaimed and
reused.

167. What is a compilation unit?
A compilation unit is a Java source code file.

168. What interface is extended by AWT event listeners?
All AWT event listeners extend the java.util.EventListener interface.

169. What restrictions are placed on method overriding?
Overridden methods must have the same name, argument list, and return type.
The overriding method may not limit the access of the method it overrides.
The overriding method may not throw any exceptions that may not be thrown
by the overridden method.

170. How can a dead thread be restarted?
A dead thread cannot be restarted.

171. What happens if an exception is not caught?
An uncaught exception results in the uncaughtException() method of the thread's ThreadGroup being invoked, which eventually results in the termination of the program in which it is thrown.

172. What is a layout manager?
A layout manager is an object that is used to organize components in a container.

173. Which arithmetic operations can result in the throwing of an ArithmeticException?
Integer / and % can result in the throwing of an ArithmeticException.

174. What are three ways in which a thread can enter the waiting state?
A thread can enter the waiting state by invoking its sleep() method, by blocking on I/O, by unsuccessfully attempting to acquire an object's lock, or by invoking an object's wait() method. It can also enter the waiting state by invoking its
(deprecated) suspend() method.

175. Can an abstract class be final?
An abstract class may not be declared as final.176. What is the ResourceBundle class?
The ResourceBundle class is used to store locale-specific resources that can be loaded by a program to tailor the program's appearance to the particular locale in which it is being run.

177. What happens if a try-catch-finally statement does not have a catch clause to handle an exception that is thrown within the body of the try statement?
The exception propagates up to the next higher level try-catch statement (if any) or results in the program's termination.

178. What is numeric promotion?
Numeric promotion is the conversion of a smaller numeric type to a larger numeric type, so that integer and floating-point operations may take place. In numerical promotion, byte, char, and short values are converted to int
values. The int values are also converted to long values, if necessary. The long and float values are converted to double values, as required.

179. What is the difference between a Scrollbar and a ScrollPane?
A Scrollbar is a Component, but not a Container. A ScrollPane is a Container. A ScrollPane handles its own events and performs its own scrolling.

180. What is the difference between a public and a non-public class?
A public class may be accessed outside of its package. A non-public class may not be accessed outside of its package.

181. To what value is a variable of the boolean type automatically initialized?
The default value of the boolean type is false.

182. Can try statements be nested?
Try statements may be tested.

183. What is the difference between the prefix and postfix forms of the ++ operator?
The prefix form performs the increment operation and returns the value of the increment operation. The postfix form returns the current value all of the expression and then performs the increment operation on that value.

184. What is the purpose of a statement block?
A statement block is used to organize a sequence of statements as a single statement group.

185. What is a Java package and how is it used?
A Java package is a naming context for classes and interfaces. A package is used to create a separate name space for groups of classes and interfaces. Packages are also used to organize related classes and interfaces into a single API unit and to control accessibility to these classes and interfaces.

186. What modifiers may be used with a top-level class?
A top-level class may be public, abstract, or final.

187. What are the Object and Class classes used for?
The Object class is the highest-level class in the Java class hierarchy. The Class class is used to represent the classes and interfaces that are loaded by a Java program.

188. How does a try statement determine which catch clause should be used to handle an exception?
When an exception is thrown within the body of a try statement, the catch clauses of the try statement are examined in the order in which they appear. The first catch clause that is capable of handling the exception is executed.
The remaining catch clauses are ignored.

189. Can an unreachable object become reachable again?
An unreachable object may become reachable again. This can happen when the object's finalize() method is invoked and the object performs an operation which causes it to become accessible to reachable objects.

190. When is an object subject to garbage collection?
An object is subject to garbage collection when it becomes unreachable to the program in which it is used.

191. What method must be implemented by all threads?
All tasks must implement the run() method, whether they are a subclass of Thread or implement the Runnable interface.

192. What methods are used to get and set the text label displayed by a Button object?
getLabel() and setLabel()

193. Which Component subclass is used for drawing and painting?
Canvas

194. What are synchronized methods and synchronized statements?
Synchronized methods are methods that are used to control access to an object. A thread only executes a synchronized method after it has acquired the lock for the method's object or class. Synchronized statements are similar to synchronized methods. A synchronized statement can only be executed after a thread has acquired the lock for the object or class referenced in the synchronized statement

195. What are the two basic ways in which classes that can be run as threads may be defined?
A thread class may be declared as a subclass of Thread, or it may implement the Runnable interface.

196. What are the problems faced by Java programmers who don't use layout managers?
Without layout managers, Java programmers are faced with determining how their GUI will be displayed across multiple windowing systems and finding a common sizing and positioning that will work within the constraints imposed by each windowing system.

197. What is the difference between an if statement and a switch statement?
The if statement is used to select among two alternatives. It uses a boolean expression to decide which alternative should be executed. The switch statement is used to select among multiple alternatives. It uses an int expression to determine which alternative should be executed.