inner class

[Manish Kumar]

public class Q {
class Question25Inner {
private static  final int i=2;
}

Question25Inner inner = new Question25Inner();
public static void main(String[] args){
Q[] q=new Q[1];
q[0]=new Q();
System.out.println(q[0].Question25Inner.i); // error
}
}

I tried to compile this code with jdk1.4 and got compile time error. I am not getting the cause for this error.
But when I compile this code with jdk1.3 on Windows98 I get some exceptions. I haven't experienced this type of exception. Please try to help me out.
Regards
-Manish
[ fixed UBB code tags ]
[ May 01, 2002: Message edited by: Jessica Sant ]

[R K Singh]

can you tell the exceptions you are getting on JDK1.3..
AW inner classes can access private members of enclosing class but outer class can not access private members of inner class.
CMIW
HTH

[alex earnshaw]

Originally posted by Manish Kumar:

public class Q {
class Question25Inner {
private static  final int i=2;
}

Question25Inner inner = new Question25Inner();
public static void main(String[] args){
Q[] q=new Q[1];
q[0]=new Q();
System.out.println(q[0].Question25Inner.i); // error
}
}

I also got error with JDK1.3

An exception has occurred in the compiler (1.3.0). Please file a bug at the Java
 Developer Connection (http://java.sun.com/cgi-bin/bugreport.cgi).  Include your
 program and the following diagnostic in your report.  Thank you.
java.lang.NullPointerException
        at com.sun.tools.javac.v8.comp.TransInner.access(TransInner.java:722)

In your println() I am not sure if it is correct to access the inner class by the class name as the class itself is not static? I think you must access the inner class by its instance name. If you change the println() as follows everything compiles and runs correctly.

public class Q
{
    static class Question25Inner
    {
        private static final int i=2;
    }

    Question25Inner inner = new Question25Inner(); //instance member of Q class
    public static void main(String[] args)
    {
        Q[] q=new Q[1];
        q[0]=new Q();
        System.out.println(q[0].inner.i); // no error now
    }
}

Can anyone else explain better why the original code doesn't work?
HTH
Alex

[Jose Botella]

In a field access expression it's possible to have:
TopLevelClass.NestedClass.field
like
System.out.println(Q.Question25Inner.i);
but it isn't possible:
variableOfTopLevelClass.NestedClass.field
like
System.out.println(q[0].Question25Inner.i);
or
System.out.println(new Q().Question25Inner.i);
the compiler error is helpful:
"
Q.java:15: unexpected type
required: class, package
found : value
"
also possible:
variableOfTopLevelClass.variableOfNestedClass.field
like
System.out.println(q[0].inner.i);
[ May 01, 2002: Message edited by: Jose Botella ]

[R K Singh]

opsssss...
first ... why the hell I did not notice class name instead of var name.....
second .. thanks Jose and all for correcting me..
Outer class can access private members of Inner class.
repeating it 10 times ...
Thanks a lot

[Manish Kumar]

But Jose compile the following code with jdk1.3

public class Q {
public  class Inner {
private static  final int i=2;
}

Inner inner = new Inner();
public static void main(String[] args){

Q inst = new Q();
System.out.println(inst.Inner.i);

}

}

This code compiles and runs without any problem with JDK1.3. But JDK1.4 gives compilation error. Is there anything about the "field access expression" in JLS ?
What should I do if I get a expression like

 
System.out.println(inst.Inner.i);
 

in the exam?
Thanks and regards
-Manish