why is main giving a preference to a method?

[sonir shah]

public class TestClass 
{ 
   public void method(Object o) 
   { 
      System.out.println("Object Version"); 
   } 
   public void method(java.io.FileNotFoundException s) 
   { 
      System.out.println("java.io.FileNotFoundException Version"); 
   }
   public void method(java.io.IOException s) 
   { 
      System.out.println("IOException Version"); 
   }
   public static void main(String args[]) 
   { 
      TestClass tc = new TestClass(); 
      tc.method(null); 
   }
}

What would be the output when the above program is compiled and run?
1)It will print "Object Version"
2) It will print "java.io.IOException version"
3)It will print "java.io.FileNotFoundException Version"
4)It will not compile
5)It will throw a runtime exception
Ans: 3)
My question is that out of the 3 methods , why did the main method only choose "java.io.FileNotFoundException Version" as the output.
Any specific reasons??
Sonir

[David Cuesta]

I think that the order of execution begin at the lower class in the tree:
Object
+-IOException
+-FileNotFoundException
byez,

[Samith Nambiar]

In such a situation the most specific parameter is chosen. Considering the hierarchy of the classes the java.io.FileNotFoundException is the most specific one and this is chosen.
Try replacing java.io.FileNotFoundException and u get a compiler error stating that the two methods
method(String s) and method(java.io.IOException s) match. This is because the compiler cannot identify the most specific one
/SAmith

[mark stone]

you guys are right. but my first instinct was to choose the method(Object o).
why, because the calling method parameter was null and null is used for objects so instinctly jumped to the method(Obejct o)
means in the exam i would have got this question as wrong !!

Originally posted by Samith Nambiar:
In such a situation the most specific parameter is chosen. Considering the hierarchy of the classes the java.io.FileNotFoundException is the most specific one and this is chosen.
Try replacing java.io.FileNotFoundException and u get a compiler error stating that the two methods
method(String s) and method(java.io.IOException s) match. This is because the compiler cannot identify the most specific one
/SAmith

[Jason Kretzer]

I would have chosen the method with the Object parameter. But this would have been my second choice after reading all the answers. My first instinct when I see null is to refer to a String.

So, the more specific the better in this case? Then why would you get the compile error between the String and the java.io.IOException methods(if you change the FNFexception to something else? Isn't java.io.IOException more specific than String?

[Junilu Lacar]

Originally posted by Jason Kretzer:
Then why would you get the compile error between the String and the java.io.IOException methods(if you change the FNFexception to something else? Isn't java.io.IOException more specific than String?

IOException and FNFException belong to the same hierarchy. That's why the compiler can determine that FNFException is more specific. IOException and String belong to different branches and the compiler will not know which branch to choose, i.e., it becomes ambiguous.