same var in parent and child interface

[Pushkaraj Thorat]

Hi i am using jdk 1.5 and compiling below code, its not giving as there is ambiguity of variable i.

interface a{
public static final int i=3;
public boolean equals1(Object obj);
}
interface b extends a{
public static final int i=30;
}

now First class is implementing b,
Output of this statement : System.out.println(((b)new First()).i);
is coming as 30
and
output of this: System.out.println(((a)new First()).i);
is coming as 3

I feel that it should show a ambiguity error
[ June 29, 2007: Message edited by: Pushkaraj Thorat ]

[Ashutosh Limaye]

class Sup 
{
public static int i=10;

}
 
public class Sub extends Sup
{
public static int i=20;
 
public static void main(String[] args) 
{
System.out.println(" "+new Sup().i);
System.out.println(" "+new Sub().i);
}
};

...this doesn't give problem why should that?

[Pushkaraj Thorat]

Its not class it should be interface.
and in interface all variables are

public static and final

and how come final variables should be allowed to change...

[Campbell Ritchie]

This seems to be something which confuses lots of people. See this recent thread. Only that was about classes.

If you have a subclass, any variables with the same name hide the variable in the superclass. You haven't altered i = 3, but only hidden it. The 3 is still there, only you can't find it.
Try this sort of thing:-

public class SuperClass implements a
{
}//end super class
. . .
System.out.println(SuperClass.a);

Then see whether this sort of thing will work, or whether it even compiles at all:-

public class SubClass extends SuperClass implements b
{
}
. . .
System.out.println(SubClass.i);
System.out.println(SuperClass.i);

Try that and tell us what happens.

[Pushkaraj Thorat]

hmm I go it
Thanks

[Campbell Ritchie]

You're welcome.

The reason it won't compile is that you have a conflict in diamond inheritance.

interface a
   |    \
   |     \
   |      Superclass
interface   |
   b        |
    \       |
     \      |
      \     |
      Subclass

Different values of i are inherited by the different routes, and the compiler cannot resolve the conflict.

[Pushkaraj Thorat]

But is there any way by which we can access the var 'i' of interface
without creating instance of interface(concrete class) and casting to interface.
[ July 02, 2007: Message edited by: Pushkaraj Thorat ]

[Campbell Ritchie]

You could try implementing one interface with an inner class . . .

But it will get you thrown out of the beginners' forum.

Anybody else got any ideas?