Interview Questions and Answers for 'Object' | Search Interview Question

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Q91. What are stateless objects ? How are they different from immutable objects ? Which of these two is thread safe ?

Object Oriented Programming

Ans. Stateless objects are the objects without instance fields (instance variables). The class may have compile time constants i.e static final fields.Immutable objects are the objects which have state but the state cannot be changed after initialization. Both are Thread safe.

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Q92. What are advantages of stateless and / or immutable objects ?

Object Oriented Programming

Ans. They can be shared across multiple threads as they are thread safe.

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Q93. What will be the output ?Integer a = 10, b =10;Integer c = 10, d = 1000;System.out.println(a == b);System.out.println(c ==d);

Core Java

Ans. truefalse

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Q94. Which of the following do you think is the primary reason you would never use a static class even the application doesn't need multiple requests or threads ?

a. Serialization
b. Runtime Polymorphism
c. Lazy Loading
d. Memory

Ans. Runtime Polymorphism

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Must know at all levels. Among Top 10 frequently asked questions in Java. Very frequently asked to fresh graduates or less experienced professionals.

Q95. What is Inheritance ?

Core Java

Ans. Its a facility for code reuse and independent extension wherein a derived class inherits the properties of parent class.

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Q96. How is static and dynamic polymorphism achieved in Java ?

Core Java

Ans. Static polymorphism is the polymorphic resolution identified at compile time and is achieved through function overloading whereas dynamic polymorphism is the polymorphic resolution identified at runtime and is achieved through method overriding.

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Q97. What will the following code print ?

Integer a = 100, b =100;
Integer c = 1000, d = 1000;
System.out.println(a == b);
System.out.println(c ==d);

Core Java

Ans. false
false

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Q98. How is multiple inheritance implemented in Java ?

Core Java

Ans. There was no multiple inheritance in java before version 8 as implementing multiple interfaces cannot be termed as inheritance.

With Java 8 , came the concept of default methods wherein the class implementing the interface carries the default implementation from the interface and hence facilitating multiple inheritance.

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Q99. Why Java is not considered pure OOP's language ?

Core Java

Ans. There are 2 reasons for it.

1. Usage of Primitive types - Though Java provides classes for the primitive data types but as the usage of primitives is permissible, its considered unpure OOP's language.

2. Usage of Static members - Static members belong to the class and not objects and hence not considered fit for pure OOP's programming.

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Q100. Can a lock be acquired on a class? How is it different than the object level lock ?

Ans. Yes, a lock can be acquired on the class. Class level lock is applicable on the whole class and hence on all objects of the class whereas the object level lock is applicable on the respective object.

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Q101. What will be the output of following ?

String str1 = new String("String1");
String str2 = new String("String1");
System.out.print(str1 == str2);
System.out.print(str1.equals(str2));
str1 = str2;
System.out.print(str1 == str2);

Core Java

a. falsetruetrue

b. truetruetrue

c. truetruefalse

d. falsetruefalse

Ans.a. falsetruetrue

Q102. What will be the output of following code ?

String str1 = "String1";
String str2 = "String1";
System.out.print(str1 == str2);
System.out.print(str1.equals(str2));
str1 = str2;
System.out.print(str1 == str2);

Core Java

a. falsetruetrue

b. falsefalsetrue

c. truetruetrue

d. falsefalsefalse

Ans.c. truetruetrue

Q103. Which of following is not the method of object class ?

Core Java

a. run

b. notify

c. wait

d. clone

Ans.a. run

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