Passing null to the overridden method when the difference between methods is the parameter subtype

Question

OUTPUT:B

Why does virtual machine call this method f(null){System.out.println("B");}?

Why not f(null){System.out.println("A");}

public class Test{

    public static class A {}
    public static class B extends A {}

    public void f(A a) {System.out.println("A");}
    public void f(B a) {System.out.println("B");}

    public static void main(String[] args) {
        new Test().f(null);
    }
}

please review your formatting ...it not clear – kTiwari Sep 27 '13 at 09:56 — kTiwari, Sep 27 '13 at 09:56
seems we need to dig out the spec again... – vikingsteve Sep 27 '13 at 09:57 — vikingsteve, Sep 27 '13 at 09:57

Prasad Kharkar · Accepted Answer · 2013-09-27T10:03:17.553

6

The method with most specific parameter type is called. Thats the rule This is from JLS section 15.12.2.5

If more than one member method is both accessible and applicable to a method invocation, it is necessary to choose one to provide the descriptor for the run-time method dispatch. The Java programming language uses the rule that the most specific method is chosen.

edited Sep 27 '13 at 10:03

answered Sep 27 '13 at 09:57

Prasad Kharkar

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Passing null to the overridden method when the difference between methods is the parameter subtype

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