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Ans. A Method that cannot be overriden in the sub class.

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Very Frequently asked.Favorite question in Walk in drive for many Indian service companies.

Q92. What is a Final Class ?

Ans. A Class that cannot be sub classed.

Sample Code for final class

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Very frequently asked. Usually asked with questions related to String. Frequently asked at CTS / Cognizant

Q93. What is an Immutable Object ?

Ans. Object that can't be changed after instantiation.

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Very Frequently asked. Usually asked along with String Class related questions.

Q94. What is an immutable class ?

Ans. Class using which only immutable (objects that cannot be changed after initialization) objects can be created.

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Q95. How to implement an immutable class ?

Ans. We can make a class immutable by

1. Making all methods and variables as private.

2. Setting variables within constructor.

Public Class ImmutableClass{

private int member;
ImmutableClass(int var){
member=var;
}
}

and then we can initialize the object of the class as

ImmutableClass immutableObject = new ImmutableClass(5);

Now all members being private , you cant change the state of the object.

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Q96. Does Declaring an object "final" makes it immutable ?

Ans. Only declaring variables as final makes them immutable. Making objects final means that the object handler cannot be used to target some other object but the object is still mutable.

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Q97. Difference between object instantiation and construction ?

Ans. Though It's often confused with each other, Object Creation ( Instantiation ) and Initialization ( Construction ) are different things in Java. Construction follows object creation.

Object Creation is the process to create the object in memory and returning its handler. Java provides New keyword for object creation.

Initialization is the process of setting the initial / default values to the members. Constructor is used for this purpose. If we don't provide any constructor, Java provides one default implementation to set the default values according to the member data types.

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Q98. Can we override static methods ? Why ?

Ans. No.

Static methods belong to the class and not the objects. They belong to the class and hence doesn't fit properly for the polymorphic behavior.

A static method is not associated with any instance of a class so the concept of overriding for runtime polymorphism using static methods is not applicable.

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Q99. Can we access instance variables within static methods ?

Ans. Yes.we cannot access them directly but we can access them using object reference.Static methods belong to a class and not objects whereas non static members are tied to an instance. Accessing instance variables without the instance handler would mean an ambiguity regarding which instance the method is referring to and hence its prohibited.

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Q100. Can we reduce the visibility of the inherited or overridden method ?

Ans. No.

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Q101. Name few Java Exceptions ?

Ans. IndexOutofBoundException ,
NoClassDefFoundException ,
OutOfMemoryException ,
IllegalArgumentException,
NullPointerException,
IllegalStateException

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Frequently asked to fresh graduates and less experienced.

Q102. Which of the following is tightly bound ? Inheritance or Composition ?

Ans. Inheritance.

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Q103. How can we make sure that a code segment gets executed even in case of uncatched exceptions ?

Ans. By putting it within finally.

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Q104. What is "super" used for ?

Ans. Used to access members of the base class.

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Q105. What is "this" keyword used for ?

Ans. Used to represent an instance of the class in which it appears.

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Q106. Difference between boolean and Boolean ?

Ans. boolean is a primitive type whereas Boolean is a class.

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Q107. What is a finalize method ?

Ans. finalize() method is called just before an object is destroyed.

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Very frequently asked in phone and walk in interviews.

Q108. What are Marker Interfaces ? Name few Java marker interfaces ?

Ans. An interface without any method declaration is called as marker interface. there are 3 in-built interfaces in JVM i.e. serializable, clonable, remote

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Q109. Is runnable a Marker interface ?

Ans. No , it has run method declared.

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Q110. Difference between Serialization and Deserialization ?

Ans. Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.

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Q111. Can we declare interface methods as private ?

Ans. With Java 9 we can declare interface methods as private

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Recently asked in Infoview Technologies.

Q112. What is a Default Constructor ?

Ans. The no argument constructor provided by Java Compiler if no constructor is specified.

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Q113. Will Compiler creates a default no argument constructor if we specify only multi argument constructor ?

Ans. No, Compiler will create default constructor only if we don't specify any constructor.

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Q114. Can we overload constructors ?

Ans. Yes.

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Q115. What will happen if we make the constructor private ?

Ans. We can't create the objects directly by invoking new operator.

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Q116. How can we create objects if we make the constructor private ?

Ans. We can do so through a static public member method or static block.

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Q117. Can we use both "this()" and "super()" in a constructor ?

Ans. No, because both this and super should be the first statement.

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Q118. Difference between nested and inner classes ?

Ans. Inner class is a type of nested class.

Inner classes are non static nested classes i.e the one that are associated with the instance of outer class.

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