Different behaviour of null ???......

Question

hi,
I am not understanding what happening in this program.
public class myString
public myString(Object oby)
          System.out.println("In Object");
public myString(String str)
          System.out.println("In String");
     public static void main(String args[])
          myString ms=new myString(null);
Whenever i run this program this prints out put as "In String"
when I comment the constructor taking String value, it gives out put as
"In Object"
can any one explain this. I doesn't understand?
Help will be much appreciated.
Thanks in advance.
Regards
Sekhar

Answer 1

I'm not really sure what happens if you have two
classes that are equally distant from object--sayC1
extends Object and C2 extends Object and one ofyour
methods takes a C1 and the other a C2--or in other
ambiguous cases. You sould look at the languagespec
and or experiment to find out.>
It's a compiler error, so no problem there :)Whoah. Man.
Freaky, but makes sene.
Yes, if you pass constant null, then it complains. However, I had the following:
    public void m1(Double s) { System.err.println("Double"); }
    public void m1(Object o) { System.err.println("Obj"); }
    public void m1(Integer i) { System.err.println("Int"); }
    public Number getNum() { return null; }
    public void m2() { m1(getNum()); }It compiled and ran. Calling m2 printed "Obj"
But if I got rid of the Object signature for m1, then it didn't compile: "cannot resolve symbol."
So I guess if your most-specific sigs are all equidistant from Object, it walks up each branch until it finds a set of equivalent sigs where there is a non-ambigous "closest-to-Object". If it doesn't find one, the compiler complains.
I don't think I've ever had to think about this for real--most or all of my cases have been pretty intuitive--but it's something to be aware of.