Java MCQ's on Method Overriding

This test contains 10 questions based on Method Overriding.
Each question answered correctly awards you 1 point and each incorrect answer has a penalty of -0.25 points, no points are deducted for unattempted answers.

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Compile time polymorphism is also known as

Method Overriding	Method Overloading
Method Rewriting	None of these

B

Comiple Time polymorphism means that methods with same names gets resolved at the compile time only. JVM does not have to resolve these methods at runtime.

Which conditions should a method satisfy to override a method of parent class. A.its return type should be same. B.number of parameters it takes should be same and of same type. C.its access specifier should not be weaker than the method to be overloaded.

Only A	Only B
Both A and B	All of the above are true.

D

For a method to override a parent class method it should satisfy all the given conditions.

What happens if we override static methods of a class.

Compile time error	Run time error
No error is thrown	None of these

C

Static methods are class level methods and are not bound to the objects, thus static methods cannot be overloaded. If we try to overload static methods, both the methods will work and can be called with the reference of the class. We wont get any sort of error.

What will be the output of the following program.

class A{
static void t(){}
}

class B extends A{

public void t(){}

}
 

Compile Time Error	Runtime Error
Code works fine	None Of these

A

Here method "t" of class B tries to override the method "t" of class A, but we cannot override a static method. Thus we will get a compile time error. When we will do A.t() the jvm will not be able to decide which method to call, the method of class A or method of class B, since both the mothods can be called with this syntax.

What will be the output of the following program ?

class A{
static void t(){}
}

class B extends A{

static void t(){}

}
 

Compile Time Error	Runtime Error
Code works fine	None Of these

C

Here we are not overring the method "t()", since method "t" is static method it can be called only with class reference, thus "A.t()" will call method of class A and "B.t()" will call the method of class B. Also you should remember that static methods are at class variables and cannot be overridden.

What will be the output of the following program ?

class A{
 public void test(){
  System.out.println("Class A");
 }
}

class B extends A{

 public void test(){
  System.out.println("Class B");
  }

 public static void main(String args[]){
  A object = new B();
  object.test(); 
 }
}
 

Compile Time Error	Runtime Error
Class A	Class B

D

This is a case of mthod overriding, method test() of class A gets overriden by method test() of class B. So at run time whenever we call test(), it will always give us method of class B.

What will be the output of the following program ?

class A{
 public void test(){
  System.out.println("Class A");
 }
}

class B extends A{

 public void test(){
  System.out.println("Class B");
  }

 public static void main(String args[]){
  B object = new A();
  object.test(); 
 }
}
 

Compile Time Error	Runtime Error
Class A	Class B

A

It will give a compile time error because we cannot give reference of a child class to the object of a parent class.

What will be the output of the following program ?

class A{
 public void test(){
  System.out.println("Class A");
 }
}

class B extends A{

 public void test(){
  System.out.println("Class B");
  }

 public static void main(String args[]){
  B object = (B)new A();
  object.test(); 
 }
}
 

Compile Time Error	Runtime Error
Class A	Class B

B

The code will comiple successfully since B object = (B)new A(); at compile time will work fine since we typecast object of class A to object of class B. But at runtime it will throw a ClassCastException since class A cannot be casted to class B.

What will be the output of the following program ?

class A{
 public void test(){
  System.out.println("Class A");
 }
}

class B extends A{

 void test(){
  System.out.println("Class B");
  }

 public static void main(String args[]){
  A object = new B();
  object.test(); 
 }
}
 

Compile Time Error	Runtime Error
Class A	Class B

A

The code will result into compile time error because it fails the condition of overriding that the access specifier of the overriding method cannot be weaker than the actual method. In our example, method test() has public access and in the class B we are tring to assign a weaker access to this method that is default, thus it will give a compile time error.

What will be the output of the following program ?

class A{
 int var = 10;
 public void test(){
  System.out.println("Class A");
 }
}

class B extends A{
 int var = 20;
 public void test(){
  System.out.println("Class B");
  }

 public static void main(String args[]){
  A object = new B();
  object.test(); 
  System.out.println(object.var);  
 }
}
 

Class A 10	Class B 10
Class A 20	Class B 20

B

The method test() gets overridden and hence object.test() will print "Class B". Variables of a class never gets overridden, thus object.var will give 10, the value of the variable in class A, because the reference of the object is of class A.

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