overloaded methods taking object arguments

[kevinn lee]

   class A{}
class B extends A{}
class C extends A{}
class D extends C{}
class Q{
void m(A r){ //1
System.out.println("m(A) "); //2
}
void m(B r){ //3
System.out.println("m(B) "); //4
}
}
class DemoA{
public static void main(String args[]){
A a1=new A(); //5
B b1=new B(); //6
C c1=new C(); //7
D d1=new D(); //8
Q q1=new Q(); //9
q1.m(c1); //10

q1.m(d1); //12
}
} 

what determines which method is called?first I expected the method taking a B object will be called since it is the closest superclass in the inheritence tree but the result was
the opposite.
what are the rules governing which method will be called in occasions like this?
thanks

[Prithvi Sehgal]

Hello,

Kevin, please QuoteYourSources for the code snippet above.

Rules are JVM will choose the closest class in the hierarchy. Why do you think that the version with method argument as B will
be called? If you look at the invocations which are

  

C c1=new C(); //7  
D d1=new D();
q1.m(c1); //10  
q1.m(d1); //12  

Here c1 is of type C and C extends A, so the closest class in the hierarchy is class A, so the version taking n A reference will be invoked.

Now line 12, we say the type which is passed is D and D extends C and C extends A, so the closest hierarchy again is A, so again the method taking
reference A will be called.

B doesn't come in hierarchy for the invocations because neither C or D extends from B, but rather directly or indirectly from A.

Hope this helps,

[Prithvi Sehgal]

Even, if you try to amend it something like this,

   

void m(Object r){ //1  
System.out.println("m(A) "); //2  
}  
void m(B r){ //3  
System.out.println("m(B) "); //4  
}  

Changed the argument to Object rather then A, still version with Object reference will be called. It is because still B has no direct or
indirect relation with class C or D.

Hope this helps,

[kevinn lee]

thanks
my bad.I had read it as if it was C & D were extended from B.
and about the source, I dont have a source to post since I found it on a hand out given by a tutor.

[Prithvi Sehgal]

Hello,

You are welcome mate.

Happy Preparation,

[Prithvi Sehgal]

Duplicate message. Sorry

[kevinn lee]

Prithvi Sehgal wrote:Duplicate message. Sorry

thanks once again for the reply