Overriding

[Pinki Roy]

public class C {

}

public class D extends C{

}

public class A {
	
	public C getOBJ(){
		System.out.println("class A - return C");
		return new C();
		
	}

}

public class B extends A{
	
	public D getOBJ(){
		System.out.println("class B - return D");
		return new D();
		
	}

}

public class Test {

public static void main(String... args) {
     A a = new B();
     a.getOBJ();
	
     }
}

Answer is class B - return D

The explanation given in the mock answers is

Explanations : From J2SE 5.0 onwards. You are now allowed to override the return type of a method with a subtype of the original type.

My problem is that but class D does not come in the hierarchy so why do we get this answer?

[Vadim Vararu]

So, till the JAVA SE5 the rule was: when you override a method, the overriding method has to return exactly the same type as the overridden one!
Beginning with JAVA SE5 the rule is: when you override a method, the overriding method has to return any type that is in relation IS-A with the type returned by the overridden method.

So, till JAVA SE5 i could not do this:

class Parent{
     public Number getNumber(){}
}

class Child extends Parent{
     public Integer getNumber(){}
}

Beginning with JAVA SE5 this is legal, because Number and Integer are covariant return types.

So, in your code the class D extends the class C, so if the overridden method returns C, it's quite legal that the overriding method returns D.

Have a good day, Vadim.

[Pinki Roy]

Vadim Vararu wrote:So, till the JAVA SE5 the rule was: when you override a method, the overriding method has to return exactly the same type as the overridden one!
Beginning with JAVA SE5 the rule is: when you override a method, the overriding method has to return any type that is in relation IS-A with the type returned by the overridden method.

So, till JAVA SE5 i could not do this:

class Parent{
     public Number getNumber(){}
}

class Child extends Parent{
     public Integer getNumber(){}
}

Beginning with JAVA SE5 this is legal, because Number and Integer are covariant return types.

So, in your code the class D extends the class C, so if the overridden method returns C, it's quite legal that the overriding method returns D.

Have a good day, Vadim.

Thanks you so much Vadim, for clearing my concept.