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Looking for the top 100 Java Interview Questions and Answers in 2014? We've compiled a list of the top 100 java technical interview questions and answers from various reputed sources and put it together in this pdf format for easy reference. Make sure to download and go through this list of the best java interview questions and answers before appearing for an interview as this pdf contains a list of the most popular java technical questions that are asked in interviews. This list includes java interview questions in the below categories: top 100 java interview questions top 100 java interview questions and answers top 100 java interview questions pdf monster top 100 interview questions top 10 java interview questions best java interview questions best java interview questions and answers site best core java interview questions top 100 interview questions on java language top 100 core java interview questions core java interview questions and answers for experienced core java interview questions pdf core java interview questions for senior developers core java interview questions and answers for freshers core java interview questions and answers pdf free download core java interview questions and answers for 2 years experienced core java interview questions for experienced candidates top 100 java interview questions with answers java interview questions and answers for freshers java interview questions and answers for experienced java interview questions and answers for 3 years experience java interview questions and answers pdf download

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Page 1: Top 100 Java Interview Questions and Answers

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JAVA

TOP 100INTERVIEW QUESTIONS & ANSWERS

Page 2: Top 100 Java Interview Questions and Answers

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Is Java platform independent?

2

QUESTION

Yes. Java is a platform independent language. We can write java code on one platform and run it on another

platform. For e.g. we can write and compile the code on windows and can run it on Linux or any other supported

platform. This is one of the main features of java.

ANSWER

QUESTION 1

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What all memory areas are allocated by JVM?

3

QUESTION

a)Class(Method) Area

b)Heap,

c) Stack,

d)Program Counter Register and

e)Native Method Stack

ANSWER

QUESTION 2

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What is class?

4

QUESTION

Class is nothing but a template that describes the data and behavior associated with instances of that class

ANSWER

QUESTION 3

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Can a .java file contain more than one java classes?

5

QUESTION

Yes. A .java file contain more than one java classes, provided at the most one of them is a public class.

ANSWER

QUESTION 4

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Different Data types in Java.

6

QUESTION

byte – 8 bit (are esp. useful when working with a stream of data from a network or a file).

short – 16 bit

char – 16 bit Unicode

int – 32 bit (whole number)

float – 32 bit (real number)

long – 64 bit (Single precision)

double – 64 bit (double precision)

ANSWER

QUESTION 5

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What is Type casting in Java?

7

QUESTION

To create a conversion between two incompatible types, we must use a cast. There are two types of casting in java:

automatic casting (done automatically) and explicit casting (done by programmer).

ANSWER

QUESTION 6

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Four main principles of OOPS language?

8

QUESTION

Inheritance

Polymorphism

Data Encapsulation

Abstraction

ANSWER

QUESTION 7

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What is Function Overriding and Overloading in Java ?

9

QUESTION

Method overloading in Java occurs when two or more methods in the same class have the exact same name, but

different parameters. On the other hand, method overriding is defined as the case when a child class redefines

the same method as a parent class. 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

ANSWER

QUESTION 8

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What is static and dynamic binding?

10

QUESTION

Binding refers to the linking of method call to its body. A binding that happens at compile time is known as static

binding while binding at runtime is known as dynamic binding.

ANSWER

QUESTION 9

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What is the difference between a synchronized method and a synchronized

block ?

11

QUESTION

In Java programming, each object has a lock. A thread can acquire the lock for an object by using the synchronized

keyword. The synchronized keyword can be applied in a method level (coarse grained lock) or block level of code

(fine grained lock)

ANSWER

QUESTION 10

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What is difference between Array and ArrayList ? When will you use Array

over ArrayList ?

12

QUESTION

The Array and ArrayListclasses differ on the following features:

a. Arrays can contain primitive or objects, while an ArrayList can contain only objects.

b. Arrays have fixed size, while an ArrayList is dynamic.

c. An ArrayListprovides more methods and features, such as addAll, removeAll, iterator, etc.

d. For a list of primitive data types, the collections use autoboxing to reduce the coding effort. However, this

approach makes them slower when working on fixed size primitive data types.

ANSWER

QUESTION 11

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What is OOPs?

13

QUESTION

Object oriented programming organizes a program around its data i,e. objects and a set of well defined interfaces to

that data. An object-oriented program can be characterized as data controlling access code

ANSWER

QUESTION 12

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What is Casting?

14

QUESTION

Casting is used to convert the value of one type to another.

ANSWER

QUESTION 13

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What is JIT compiler?

15

QUESTION

Just-In-Time(JIT) compiler:It is used to improve the performance. JIT compiles parts of the byte code that have

similar functionality at the same time, and hence reduces the amount of time needed for compilation.Here the

term “compiler” refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set

of a specific CPU.

ANSWER

QUESTION 14

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What is the main difference between Java platform and other platforms?

16

QUESTION

The Java platform differs from most other platforms in the sense that it's a software-based platform that runs on top

of other hardware-based platforms. It has two components:

1. Runtime Environment

2. API(Application Programming Interface)

ANSWER

QUESTION 15

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What are Constructors?

17

QUESTION

Constructors are used for creating an instance of a class, they are invoked when an instance of class gets created.

Constructor name and class name should be same and it doesn’t have a return type

ANSWER

QUESTION 16

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What is default and parameterized constructors?

18

QUESTION

Default: Constructors with no arguments are known as default constructors, when you don’t declare any constructor

in a class, compiler creates a default one automatically.

Parameterized: Constructor with arguments are known as parameterized constructors.

ANSWER

QUESTION 17

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What is difference between aggregation and composition?

19

QUESTION

Aggregation represents weak relationship whereas composition represents strong relationship. For example: bike

has an indicator (aggregation) but bike has an engine (compostion).

ANSWER

QUESTION 18

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What are Encapsulation, Inheritance and Polymorphism?

20

QUESTION

Encapsulation is the mechanism that binds together code and data it manipulates and keeps both safe from outside

interference and misuse. Inheritance is the process by which one object acquires the properties of another object.

Polymorphism is the feature that allows one interface to be used for general class actions.

ANSWER

QUESTION 19

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What is final, finalize() and finally?

21

QUESTION

final : final keyword can be used for class, method and variables. A final class cannot be subclassed and it prevents

other programmers from subclassing a secure class to invoke insecure methods. A final method can’t be

overridden. A final variable can’t change from its initialized value.

finalize() : finalize() method is used just before an object is destroyed and can be called just prior to garbage

collection.

finally : finally, a key word used in exception handling, creates a block of code that will be executed after a try/catch

block has completed and before the code following the try/catch block. The finally block will execute whether or

not an exception is thrown. For example, if a method opens a file upon exit, then you will not want the code that

closes the file to be bypassed by the exception-handling mechanism. This finally keyword is designed to address

this contingency.

ANSWER

QUESTION 20

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What is Garbage Collection and how to call it explicitly?

22

QUESTION

When an object is no longer referred to by any variable, java automatically reclaims memory used by that object.

This is known as garbage collection. System. gc() method may be used to call it explicitly.

ANSWER

QUESTION 21

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What is meant by Inheritance and what are its advantages?

23

QUESTION

Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of

code and accessibility of variables and methods of the super class by subclasses.

ANSWER

QUESTION 22

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What is the difference between superclass and subclass?

24

QUESTION

A super class is a class that is inherited whereas sub class is a class that does the inheriting.

ANSWER

QUESTION 23

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What is the difference between Integer and int?

25

QUESTION

a) Integer is a class defined in the java. lang package, whereas int is a primitive data type defined in the Java

language itself. Java does not automatically convert from one to the other.

b) b) Integer can be used as an argument for a method that requires an object, whereas int can be used for

calculations.

ANSWER

QUESTION 24

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How do I serialize an object to a file?

26

QUESTION

The class whose instances are to be serialized should implement an interface Serializable. Then you pass the

instance to the ObjectOutputStream which is connected to a fileoutputstream. This will save the object to a file.

ANSWER

QUESTION 25

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What is the difference between String and String Buffer?

27

QUESTION

a) String objects are constants and immutable whereas StringBuffer objects are not.

b) b) String class supports constant strings whereas StringBuffer class supports growable and modifiable strings.

ANSWER

QUESTION 26

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What is the difference between Array and vector?

28

QUESTION

Array is a set of related data type and static whereas vector is a growable array of objects and dynamic.

ANSWER

QUESTION 27

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What is source and listener?

29

QUESTION

source : A source is an object that generates an event. This occurs when the internal state of that object changes in

some way.

listener : A listener is an object that is notified when an event occurs. It has two major requirements. First, it must

have been registered with one or more sources to receive notifications about specific types of events. Second, it

must implement methods to receive and process these notifications.

ANSWER

QUESTION 28

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What is Thread in Java?

30

QUESTION

Thread is an independent path of execution. It's way to take advantage of multiple CPU available in a machine. By

employing multiple threads you can speed up CPU bound task. For example, if one thread takes 100 millisecond

to do a job, you can use 10 thread to reduce that task into 10 millisecond. Java provides excellent support for

multi-threading at language level, and its also one of strong selling point.

ANSWER

QUESTION 29

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What is FutureTask in Java?

31

QUESTION

FutureTask represents a cancellable asynchronous computation in concurrent Java application. This class provides

a base implementation of Future, with methods to start and cancel a computation, query to see if the computation

is complete, and retrieve the result of the computation. The result can only be retrieved when the computation has

completed; the get methods will block if the computation has not yet completed. A FutureTask object can be used

to wrap a Callable or Runnable object. Since FutureTask also implements Runnable, it can be submitted to an

Executor for execution.

ANSWER

QUESTION 30

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There are three threads T1, T2 and T3? How do you ensure sequence T1,

T2, T3 in Java?

32

QUESTION

Sequencing in multi-threading can be achieved by different means but you can simply use join() method of thread

class to start a thread when another one is finished its execution. To ensure three threads execute you need to

start the last one first e.g. T3 and then call join methods in reverse order e.g. T3 calls T2. join, and T2 calls

T1.join, this ways T1 will finish first and T3 will finish last.

ANSWER

QUESTION 31

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What is blocking method in Java?

33

QUESTION

A blocking method is a method which blocks until task is done, for example accept() method of ServerSocket blocks

until a client is connected. here blocking means control will not return to caller until task is finished. On the other

hand there are asynchronous or non-blocking method which returns even before task is finished.

ANSWER

QUESTION 32

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Difference between volatile and atomic variable in Java?

34

QUESTION

This is an interesting question for Java programmer, at first, volatile and atomic variable look very similar, but they

are different. Volatile variable provides you happens-before guarantee that a write will happen before any

subsequent write, it doesn't guarantee atomicity. For example count++ operation will not become atomic just by

declaring count variable as volatile. On the other handAtomicInteger class provides atomic method to perform

such compound operation atomically e.g. getAndIncrement() is atomic replacement of increment operator. It can

be used to atomically increment current value by one. Similarly you have atomic version for other data type and

reference variable as well.

ANSWER

QUESTION 33

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What is the Difference between JDK and JRE?

35

QUESTION

The “JDK” is the Java Development Kit. I.e., the JDK is bundle of software that you can use to develop Java based

software.

The “JRE” is the Java Runtime Environment. I.e., the JRE is an implementation of the Java Virtual Machine which

actually executes Java programs.

Typically, each JDK contains one (or more) JRE’s along with the various development tools like the Java source

compilers, bundling and deployment tools, debuggers, development libraries, etc.

ANSWER

QUESTION 34

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What is Annotation in Java?

36

QUESTION

An annotation, in the java programming language is a special form of syntactic metadata that can be added to Java

Source Code.

Classes, methods, variables parameters and packages may be annotated.

Unlike Java doc tags, Java annotation are reflective, in that they are embedded in class files generated by the

compiler and may be retained by the java VM to make retrievable at run-time. Annotation is basically to attach

metadata to method, class or package. Metadata is used by the compiler to perform some basic compile-time

checking.

ANSWER

QUESTION 35

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Explain Java Thread Life cycle.

37

QUESTION

The life cycle of threads in Java is very similar to the life cycle of processes running in an operating system. During its life

cycle the thread moves from one state to another depending on the operation performed by it or performed on it. A Java

thread can be in one of the following states:

• NEW: A thread that is just instantiated is in new state. When a start () method is invoked, the thread moves to the ready

state from which it is automatically moved to runnable state by the thread scheduler.

• RUNNABLE (ready_running) A thread executing in the JVM is in running state.

• BLOCKED A thread that is blocked waiting for a monitor lock is in this state. This can also occur when a thread performs

an I/O operation and moves to next (runnable) state.

• WAITING A thread that is waiting indefinitely for another thread to perform a particular action is in this state.

• TIMED_WAITING (sleeping) A thread that is waiting for another thread to perform an action up to a specified waiting time

is in this state.

• TERMINATED (dead) A thread that has exited is in this state.

ANSWER

QUESTION 36

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Which way a developer should use for creating thread, i.e. Sub classing

Thread or implementing Runnable.

38

QUESTION

There are two ways of creating Thread in java (i.e. sub classing or implementing Runnable). It is very important to

understand the implication of using these two approaches.

There are two different points about using these two approaches.

• By extending the thread class, the derived class itself is a thread object and it gains full control over the thread life cycle.

Implementing the Runnable interface does not give developers any control over the thread itself, as it simply defines the

unit of work that will be executed in a thread.

• Another important point is that when extending the Thread class, the derived class cannot extend any other base classes

because Java only allows single inheritance. By implementing the Runnable interface, the class can still extend other

base classes if necessary.

To summarize, if developer needs a full control over the Thread life cycle, sub classing Thread class is a good choice, and if

programs need more flexibility by extending other class developer, should go with implementing Runnable interface.

ANSWER

QUESTION 37

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What is the use of volatile in Java?

39

QUESTION

Threads are allowed to hold the values of variables in local memory (e.g. in a machine register).

If a variable is marked as volatile, every time when the variable is used, it must be read from the main memory,

similarly every time the variable is written, the value must be stored in main memory.

ANSWER

QUESTION 38

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What is Downcasting ?

40

QUESTION

Downcasting means casting from a general to a more specific type.

ANSWER

QUESTION 39

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What is the difference between a constructor and a method?

41

QUESTION

Method is just an ordinary member function which consists of its own return type (can be a void), name and always

invoked by a dot operator whereas a constructor is the member function of that class which is used to create

objects in it, the name of the class and constructor is always same, no return type and always invoked by a new

operator.

ANSWER

QUESTION 40

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What is the common usage of serialization? What exceptions occur during

serialization?

42

QUESTION

The object need to be serialized when it’s sent over a network and when it’s state is saved. Exceptions which occur

during serialization are:

a. transient fields

b. when the base class is serialized then only base class fields are handled.

c. Static fields are ignored because they are not part of any state.

ANSWER

QUESTION 41

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What is the difference between preemptive scheduling and time slicing?

43

QUESTION

Under preemptive scheduling, is the highest priority task which is executed until it enters the waiting or dead states

or a higher priority task. 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.

ANSWER

QUESTION 42

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How applets communicate with each other?

44

QUESTION

Applets may communicate with other applets running in the same virtual machine but it’s not necessary that they

communicate. If the applets are of the same class, they can communicate via shared static variables. If the

applets are of different classes, then each will need a reference to the same class with static variables. In any

case the basic idea is to pass the information back and forth through a static variable.

ANSWER

QUESTION 43

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What is the similarity between Dynamic Binding and linking?

45

QUESTION

Dynamic binding is orthogonal to dynamic linking. Binding refers to the linking of a procedure call to the code to be

executed in response to the call. Dynamic binding It is associated with polymorphism and inheritance, it(also

known as late binding) means that the code associated with a given procedure call is not known until the time of

the call at run-time.

ANSWER

QUESTION 44

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How are Observer and Observable used?

46

QUESTION

List of observers are maintained by the objects that are subclasses the observable class. 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.

ANSWER

QUESTION 45

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What is the difference between an Inner Class and a Sub-Class?

47

QUESTION

An Inner class is a class which is nested within another class. An Inner class has access rights for the class which is

nesting it and it can access all variables and methods defined in the outer class.

A sub-class is a class which inherits from another class called super class. Sub-class can access all public and

protected methods and fields of its super class

ANSWER

QUESTION 46

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What is data encapsulation and what’s its significance?

48

QUESTION

Encapsulation is a concept in Object Oriented Programming for combining properties and methods in a single unit.

Encapsulation helps programmers to follow a modular approach for software development as each object has its

own set of methods and variables and serves its functions independent of other objects. Encapsulation also

serves data hiding purpose.

ANSWER

QUESTION 47

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What is a singleton class? Give a practical example of its usage.

49

QUESTION

A singleton class in java can have only one instance and hence all its methods and variables belong to just one

instance. Singleton class concept is useful for the situations when there is a need to limit the number of objects for

a class.

The best example of singleton usage scenario is when there is a limit of having only one connection to a database

due to some driver limitations or because of any licensing issues.

ANSWER

QUESTION 48

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What are Loops in Java? What are three types of loops?

50

QUESTION

Looping is used in programming to execute a statement or a block of statement repeatedly. There are three types of loops in

Java:

1) For Loops

For loops are used in java to execute statements repeatedly for a given number of times. For loops are used when number

of times to execute the statements is known to programmer.

2) While Loops

While loop is used when certain statements need to be executed repeatedly until a condition is fulfilled. In while loops,

condition is checked first before execution of statements.

3) Do While Loops

Do While Loop is same as While loop with only difference that condition is checked after execution of block of statements.

Hence in case of do while loop, statements are executed at least once.

ANSWER

QUESTION 49

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What is the difference between continue and break statement?

51

QUESTION

break and continue are two important keywords used in Loops. When a break keyword is used in a loop, loop is

broken instantly while when continue keyword is used, current iteration is broken and loop continues with next

iteration

ANSWER

QUESTION 50

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What is ternary operator? Give an example.

52

QUESTION

Ternary operator, also called conditional operator is used to decide which value to assign to a variable based on a

Boolean value evaluation. It’s denoted as?

In the below example, if rank is 1, status is assigned a value of “Done” else “Pending”.

ANSWER

QUESTION 51

1234567

public class conditionTest {public static void main(string args[]) {String status;int rank;status= (rank == 1) ? "Done": "Pending";}}

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What are 6 different types of operators in Java?

53

QUESTION

In java, operators can be classified in following six types:

• Arithmetic Operators

Used for arithmetic calculations. E.g. +,-,*,/,%,++,–

• Relational Operators

Used for relational comparison. E.g. ==,!=, >,<,<=,>=

• Bitwise operators

Used for bit by bit operations. E.g. &,|,^,~

• Logical Operators

Used for logical comparisons. E.g. &&,||,!

• Assignment Operators

Used for assigning values to variables. E.g. =,+=,-=,*=,/=

ANSWER

QUESTION 52

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What’s the base class in Java from which all classes are derived?

54

QUESTION

java.lang.object

ANSWER

QUESTION 53

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When the constructor of a class is invoked?

55

QUESTION

The constructor of a class is invoked every time an object

is created with new keyword. For example, in the

following class two objects are created using new

keyword and hence, constructor is invoked two times.

1 public class const_example {

2

3 const_example() {

4

5 System.out.println("Inside constructor");

6

7 }

8

9 Public static void main(String args[]) {

10

11 const_example c1=new const_example();

12

13 const_example c2=new const_example();

14

15 }

16

17 }

ANSWER

QUESTION 54

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Can we override static methods of a class?

56

QUESTION

We cannot override static methods. Static methods belong to a class and not to individual objects and are resolved

at the time of compilation (not at runtime).Even if we try to override static method,we will not get an complitaion

error,nor the impact of overriding when running the code.

ANSWER

QUESTION 55

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Is String a data type in java?

57

QUESTION

String is not a primitive data type in java. When a string is created in java, it’s actually an object of Java.Lang.String

class that gets created. After creation of this string object, all built-in methods of String class can be used on the

string object.

ANSWER

QUESTION 56

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What is multi-threading?

58

QUESTION

Multi threading is a programming concept to run multiple tasks in a concurrent manner within a single program.

Threads share same process stack and running in parallel. It helps in performance improvement of any program.

ANSWER

QUESTION 57

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How objects of a class are created if no constructor is defined in the class?

59

QUESTION

Even if no explicit constructor is defined in a java class, objects get created successfully as a default constructor is

implicitly used for object creation. This constructor has no parameters.

ANSWER

QUESTION 58

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Give an example of use of Pointers in Java class.

60

QUESTION

There are no pointers in Java. So we can’t use concept of pointers in Java.

ANSWER

QUESTION 59

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What’s difference between Stack and Queue?

61

QUESTION

Stack and Queue both are used as placeholder for a collection of data. The primary difference between a stack and

a queue is that stack is based on Last in First out (LIFO) principle while a queue is based on FIFO (First In First

Out) principle.

ANSWER

QUESTION 60

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What are the two environment variables that must be set in order to run

any Java programs?

62

QUESTION

Java programs can be executed in a machine only once following two environment variables have been properly

set:

1. PATH variable

2. CLASSPATH variable

ANSWER

QUESTION 61

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What are checked exceptions?

63

QUESTION

Checked exception are those which the Java compiler forces you to catch.Example:IOException are checked

exceptions.

ANSWER

QUESTION 62

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What are runtime exceptions?

64

QUESTION

Runtime exceptions are those exceptions that are thrown at runtime because of either wrong input data or because

of wrong business logic etc. These are not checked by the compiler at compile time.

ANSWER

QUESTION 63

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What are wrapper classes?

65

QUESTION

Java provides specialized classes corresponding to each of the primitive data types. These are called wrapper

classes.They are example: Integer, Character, Double etc.

ANSWER

QUESTION 64

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What is an abstract class?

66

QUESTION

Abstract class must be extended/subclassed (to be useful). It serves as a template. A class that is abstract may not

be instantiated (ie. you may not call its constructor), abstract class may contain static data.Any class with an

abstract method is automatically abstract itself, and must be declared as such. A class may be declared abstract

even if it has no abstract methods. This prevents it from being instantiated.

ANSWER

QUESTION 65

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What is the default value of the local variables?

67

QUESTION

The local variables are not initialized to any default value, neither primitives nor object references. If you try to use

these variables without initializing them explicitly, the java compiler will not compile the code. It will complain abt

the local varaible not being initilized.

ANSWER

QUESTION 66

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What is the difference between a Choice and a List?

68

QUESTION

A Choice is displayed in a compact form that must be pulled down, in order for a user to be able to see the list of all

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.

ANSWER

QUESTION 67

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What is clipping?

69

QUESTION

Clipping is defined as the process of confining paint operations to a limited area or shape.

ANSWER

QUESTION 68

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Does Java support multiple inheritance?

70

QUESTION

No, Java does not support multiple inheritance. Each class is able to extend only on one class, but is able to

implement more than one interfaces.

ANSWER

QUESTION 69

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What’s a deadlock ?

71

QUESTION

A condition that occurs when two processes are waiting for each other to complete, before proceeding. The result is

that both processes wait endlessly.

ANSWER

QUESTION 70

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What is difference between Path and Classpath ?

72

QUESTION

Path and Classpath are operating system level environment variales. Path is used define where the system can find

the executables(.exe) files and classpath is used to specify the location .class files.

ANSWER

QUESTION 71

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What are instance variables ?

73

QUESTION

Instance variables are those which are defined at the class level. Instance variables need not be initialized before

using them as they are automatically initialized to their default values.

ANSWER

QUESTION 72

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How to define a constant variable in Java ?

74

QUESTION

The variable should be declared as static and final. So only one copy of the variable exists for all instances of the

class and the value can’t be changed also. static final int PI = 2.14; is an example for constant.

ANSWER

QUESTION 73

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Can a class be declared as protected ?

75

QUESTION

The protected access modifier cannot be applied to class and interfaces. Methods, fields can be declared protected,

however methods and fields in a interface cannot be declared protected.

ANSWER

QUESTION 74

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What is the access scope of a protected method ?

76

QUESTION

A protected method can be accessed by the classes within the same package or by the subclasses of the class in

any package.

ANSWER

QUESTION 75

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What are the restriction imposed on a static method or a static block of code ?

77

QUESTION

A static method should not refer to instance variables without creating an instance and cannot use “this” operator to

refer the instance.

ANSWER

QUESTION 76

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Can we declare a static variable inside a method ?

78

QUESTION

Static varaibles are class level variables and they can’t be declared inside a method. If declared, the class will not

compile.

ANSWER

QUESTION 77

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Can a method inside a Interface be declared as final ?

79

QUESTION

No not possible. Doing so will result in compilation error. public and abstract are the only applicable modifiers for

method declaration in an interface.

ANSWER

QUESTION 78

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Why is an Interface be able to extend more than one Interface but a Class can’t extend

more than one Class ?

80

QUESTION

Basically Java doesn’t allow multiple inheritance, so a Class is restricted to extend only one Class. But an Interface

is a pure abstraction model and doesn’t have inheritance hierarchy like classes(do remember that the base class

of all classes is Object). So an Interface is allowed to extend more than one Interface.

ANSWER

QUESTION 79

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What are wrapper classes?

81

QUESTION

Java provides specialized classes corresponding to each of the primitive data types. These are called wrapper

classes. They are e.g. Integer, Character, Double etc.

ANSWER

QUESTION 80

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Under what circumstances might you use the yield method of the Thread class

82

QUESTION

-To call from the currently running thread to allow another thread of the same or higher priority to run

-To call on a waiting thread to allow it to run

-To allow a thread of higher priority to run

-To call from the currently running thread with a parameter designating which thread should be allowed to run

ANSWER

QUESTION 81

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If I want an object of my class to be thrown as an exception object, what should I

do?

83

QUESTION

The class should extend from Exception class. Or you can extend your class from some more precise exception

type also

ANSWER

QUESTION 82

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How are Observer and Observable used?

84

QUESTION

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.

ANSWER

QUESTION 83

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If a class is declared without any access modifiers, where may the class be

accessed?

85

QUESTION

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.

ANSWER

QUESTION 84

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What is the purpose of the finally clause of a try-catch-finally statement?

86

QUESTION

The finally clause is used to provide the capability to execute code no matter whether or not an exception is thrown

or caught.

ANSWER

QUESTION 85

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Can a double value be cast to a byte?

87

QUESTION

Yes, a double value can be cast to a byte.

ANSWER

QUESTION 86

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What must a class do to implement an interface?

88

QUESTION

It must provide all of the methods in the interface and identify the interface in its implements clause.

ANSWER

QUESTION 87

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What are cookies and how will you use them?

89

QUESTION

Cookies are a mechanism that a servlet uses to have a client hold a small amount of state-information associated

with the user. a) Create a cookie with the Cookie constructor: public Cookie(String name, String value)

b) A servlet can send a cookie to the client by passing a Cookie object to the addCookie() method of

HttpServletResponse: public void HttpServletResponse. addCookie(Cookie cookie)

c) A servlet retrieves cookies by calling the getCookies() method of HttpServletRequest: public Cookie[ ]

HttpServletRequest. getCookie().

ANSWER

QUESTION 88

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What is Servlet chaining?

90

QUESTION

Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. In servlet

chaining, one servlet’s output is piped to the next servlet’s input. This process continues until the last servlet is

reached. Its output is then sent back to the client.

ANSWER

QUESTION 89

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What is the difference between TCP/IP and UDP?

91

QUESTION

TCP/IP is a two-way communication between the client and the server and it is a reliable and there is a confirmation

regarding reaching the message to the destination. It is like a phone call. UDP is a one-way communication only

between the client and the server and it is not a reliable and there is no confirmation regarding reaching the

message to the destination. It is like a postal mail.

ANSWER

QUESTION 90

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For which statements does it make sense to use a label?

92

QUESTION

The only statements for which it makes sense to use a label are those statements that can enclose

a break orcontinue statement.

ANSWER

QUESTION 91

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How are the elements of a CardLayout organized?

93

QUESTION

The elements of a CardLayout are stacked, one on top of the other, like a deck of cards

ANSWER

QUESTION 92

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What is the difference between a while statement and a do while statement?

94

QUESTION

A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do

while statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do

whilestatement will always execute the body of a loop at least once.

ANSWER

QUESTION 93

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When does the compiler supply a default constructor for a class?

95

QUESTION

The compiler supplies a default constructor for a class if no other constructors are provided.

ANSWER

QUESTION 94

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What is Domain Naming Service(DNS)?

96

QUESTION

It is very difficult to remember a set of numbers(IP address) to connect to the Internet. The Domain Naming

Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For

example, www. mascom. com implies com is the domain name reserved for US commercial sites, moscom is the

name of the company and www is the name of the specific computer, which is mascom’s server.

ANSWER

QUESTION 95

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What is a Jar file?

97

QUESTION

Jar file allows to efficiently deploying a set of classes and their associated resources. The elements in a jar file are

compressed, which makes downloading a Jar file much faster than separately downloading several

uncompressed files. The package java. util. zip contains classes that read and write jar files.

ANSWER

QUESTION 96

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What are JSP Directives?

98

QUESTION

A JSP directive affects the overall structure of the servlet class. It usually has the following form:<%@ directive

attribute=”value” %> However, you can also combine multiple attribute settings for a single directive, as

follows:<%@ directive attribute1=”value1″ attribute 2=”value2″ . . . attributeN =”valueN” %> There are two main

types of directive: page, which lets to do things like import classes, customize the servlet superclass, and the like;

and include, which lets to insert a file into the servlet class at the time the JSP file is translated into a servlet

ANSWER

QUESTION 97

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How can I set a cookie in JSP?

99

QUESTION

response. setHeader(”Set-Cookie”, “cookie string”); To give the response-object to a bean, write a method

setResponse (HttpServletResponse response) - to the bean, and in jsp-file:<% bean. setResponse (response);

%>

ANSWER

QUESTION 98

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What is numeric promotion?

100

QUESTION

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.

ANSWER

QUESTION 99

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How are Servlets and JSP Pages related?

101

QUESTION

JSP pages are focused around HTML (or XML) with Java codes and JSP tags inside them. When a web server that

has JSP support is asked for a JSP page, it checks to see if it has already compiled the page into a servlet. Thus,

JSP pages become servlets and are transformed into pure Java and then compiled, loaded into the server and

executed.

ANSWER

QUESTION 100

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List of Resources

102

http://top100interviewquestions.com/java-basics-part1/http://www.javacodegeeks.com/2014/04/java-interview-questions-and-answers.html#2http://beginnersbook.com/2013/05/java-interview-questions/#h3http://www.slideshare.net/p2cinfotech/java-frequently-asked-interview-questions-and-answershttp://www.javatpoint.com/corejava-interview-questions-1http://www.techinterviews.com/master-list-of-java-interview-questionshttp://javarevisited.blogspot.com/2014/07/top-50-java-multithreading-interview-questions-answers.htmlhttps://www.udemy.com/blog/java-interview-questions/http://careerride.com/Interview-Questions-Core-Java.aspxhttp://career.guru99.com/top-100-core-java-interview-questions/1/http://careerbaba.in/2014/01/top-50-core-java-interview-questions-and-answers/

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