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Object oriented programming Java

Which of this keyword must be used to inherit a class?
a) super
b) this
c) extent
d) extends

Answer: d


A class member declared protected becomes a member of subclass of which type?
a) public member
b) private member
c) protected member
d) static member

Answer: b


Which of these is correct way of inheriting class A by class B?
a) class B + class A {}
b) class B inherits class A {}
c) class B extends A {}
d) class B extends class A {}

Answer: c


Which two classes use the Shape class correctly?

A. public class Circle implements Shape 

   {

    private int radius;

   }

B. public abstract class Circle extends Shape 

   {

    private int radius;

   }

C. public class Circle extends Shape 

   {

   private int radius;

   public void draw();

   }

D. public abstract class Circle implements Shape 

   {

    private int radius;

    public void draw();

   }

E. public class Circle extends Shape 

   {

    private int radius;

    public void draw()

    {

     /* code here */

    }

   }

F. public abstract class Circle implements Shape 

   {

     private int radius;

     public void draw() 

     { 

      /* code here */ 

     }

   }

a)B,E
b)A,C
c)C,E
d)T,H

Answer: a

What will be the output of the following Java program?

  1.     class

  2.     {

  3.         int i;

  4.         void display() 

  5.         {

  6.             System.out.println(i);

  7.         }

  8.     }    

  9.     class B extends

  10.     {

  11.         int j;

  12.         void display() 

  13.         {

  14.             System.out.println(j);

  15.         }

  16.     }    

  17.     class inheritance_demo 

  18.     {

  19.         public static void main(String args[])

  20.         {

  21.             B obj = new B();

  22.             obj.i=1;

  23.             obj.j=2;   

  24.             obj.display();     

  25.         }

  26.    }

a) 0
b) 1
c) 2
d) Compilation Error

Answer: c

What is not type of inheritance?
a) Single inheritance
b) Double inheritance
c) Hierarchical inheritance
d) Multiple inheritance

Answer: b

Using which of the following, multiple inheritance in Java can be implemented?
a) Interfaces
b) Multithreading
c) Protected methods
d) Private methods

Answer: a

All classes in Java are inherited from which class?
a) java.lang.class
b) java.class.inherited
c) java.class.object
d) java.lang.Object

Answer: d

 In order to restrict a variable of a class from inheriting to subclass, how variable should be declared?
a) Protected
b) Private
c) Public
d) Static

Answer: b

 If super class and subclass have same variable name, which keyword should be used to use super class?
a) super
b) this
c) upper
d) classname

Answer: a

Static members are not inherited to subclass.
a) True
b) False

Answer: b

 Which of the following is used for implementing inheritance through an interface?
a) inherited
b) using
c) extends
d) implements

Answer: d

Which of the following is used for implementing inheritance through class?
a) inherited
b) using
c) extends
d) implements

Answer: c

What would be the result if a class extends two interfaces and both have a method with same name and signature? Lets assume that the class is not implementing that method.
a) Runtime error
b) Compile time error
c) Code runs successfully
d) First called method is executed successfully

Answer: b

Does Java support multiple level inheritance?
a) True
b) False

Answer: a

Which of these keywords are used to define an abstract class?
a) abst
b) abstract
c) Abstract
d) abstract class

Answer: b

Which of these is not abstract?
a) Thread
b) AbstractList
c) List
d) None of the Mentioned

Answer: a

 If a class inheriting an abstract class does not define all of its function then it will be known as?
a) Abstract
b) A simple class
c) Static class
d) None of the mentioned

Answer: a

Which of these is not a correct statement?
a) Every class containing abstract method must be declared abstract
b) Abstract class defines only the structure of the class not its implementation
c) Abstract class can be initiated by new operator
d) Abstract class can be inherited

Answer: c

Which of these packages contains abstract keyword?
a) java.lang
b) java.util
c) java.io
d) java.system

Answer: a

 What will be the output of the following Java code?

  1.     class

  2.     {

  3.         public int i;

  4.         private int j;

  5.     }    

  6.     class B extends

  7.     {

  8.         void display() 

  9.         {

  10.             super.j = super.i + 1;

  11.             System.out.println(super.i + " " + super.j);

  12.         }

  13.     }    

  14.     class inheritance 

  15.    {

  16.         public static void main(String args[])

  17.         {

  18.             B obj = new B();

  19.             obj.i=1;

  20.             obj.j=2;   

  21.             obj.display();     

  22.         }

  23.    }

  1. 2 2
    b) 3 3
    c) Runtime Error
    d) Compilation Error

Answer: d

 

What will be the output of the following Java code?

  1.     class

  2.     {

  3.         int i;

  4.         void display() 

  5.         {

  6.             System.out.println(i);

  7.         }

  8.     }    

  9.     class B extends

  10.     {

  11.         int j;

  12.         void display() 

  13.         {

  14.             System.out.println(j);

  15.         }

  16.     }    

  17.     class method_overriding 

  18.     {

  19.         public static void main(String args[])

  20.         {

  21.             B obj = new B();

  22.             obj.i=1;

  23.             obj.j=2;   

  24.             obj.display();     

  25.         }

  26.    }

a)0
b)1
c)2
d) Compilation Error

Answer: c

 What will be the output of the following Java code?

  1.     class

  2.     {

  3.         public int i;

  4.         protected int j;

  5.     }    

  6.     class B extends

  7.     {

  8.         int j;

  9.         void display() 

  10.         {

  11.             super.j = 3;

  12.             System.out.println(i + " " + j);

  13.         }

  14.     }    

  15.     class Output 

  16.     {

  17.         public static void main(String args[])

  18.         {

  19.             B obj = new B();

  20.             obj.i=1;

  21.             obj.j=2;   

  22.             obj.display();     

  23.         }

  24.    }

a)12
b)21
c)13
d) 3 1

Answer: a

 

POLYMORPHISM

Which of the following is not OOPS concept in Java?
a) Inheritance
b) Encapsulation
c) Polymorphism
d) Compilation

Answer: d

 

Which of the following is a type of polymorphism in Java?
a) Compile time polymorphism
b) Execution time polymorphism
c) Multiple polymorphism
d) Multilevel polymorphism

Answer: a

 

 When does method overloading is determined?
a) At run time
b) At compile time
c) At coding time
d) At execution time

Answer: b

 

When Overloading does not occur?
a) More than one method with same name but different method signature and different number or type of parameters
b) More than one method with same name, same signature but different number of signature
c) More than one method with same name, same signature, same number of parameters but different type
d) More than one method with same name, same number of parameters and type but different signature

Answer: d

 

Which concept of Java is a way of converting real world objects in terms of class?
a) Polymorphism
b) Encapsulation
c) Abstraction
d) Inheritance

Answer: c

 

Which concept of Java is achieved by combining methods and attribute into a class?
a) Encapsulation
b) Inheritance
c) Polymorphism
d) Abstraction

Answer: a

 

Method overriding is combination of inheritance and polymorphism?
a) True
b) false

Answer: a

 

 



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