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overriding question

 
Ranch Hand
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class A { }

class B extends A { }

class C extends B {
static void doSomething ( A x , A y ) {System.out.print("AA");}
static void doSomething ( A x , B y ) {System.out.print("AB");}
static void doSomething ( B x , A y ) {System.out.print("BA");}
static void doSomething ( B x , B y ) {System.out.print("BB");}
static void doSomething ( C x , C y ) { System.out.println("CC");}

public static void main(String[] args) {
doSomething(null,null);
}
}


it prints cc , can anyone tell me how this happens.
thanks
 
Sheriff
Posts: 11343
Mac Safari Java
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This is a case of the "most specific" method being selected.

A null reference can represent any object type, so it can match any non-primitive argument type.

In this case, the choices are A, B, and C (in various combinations). A null reference could represent any of these. But C is "more specific" than B because a C reference can be upcast to type B, but not vice versa. Likewise, B is more specific than A. So the most specific choice here is the method that takes two C references.

For other examples, search this forum for "most specific."

(For the dirty details, see JLS - 15.12.2.5 Choosing the Most Specific Method.)
 
marc weber
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PS: These methods are overloaded -- not overridden.
 
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