Reference static var of static nested from Outer

[Cathy Song]

 
    public class OuterReferVarOfStaticInner {
       static class StaticInner {
         static int i=100;
      }
      
       public static void main(String[] args) {
         OuterReferVarOfStaticInner tt = new OuterReferVarOfStaticInner();
         //int j= tt.new StaticInner().i; //error line 1
         int j = OuterReferVarOfStaticInner.StaticInner.i; //line 2 ok
         System.out.println(j);
      }
   }

Why does line 1 not compile?
Thanks.

[Joel McNary]

What error are you getting? This compiled fine for me...

[Vad Fogel]

The line causing an error is commented out.

[Harwinder Bhatia]

Cathy
No error for me either.
Ofcourse with line 1 uncommented and removing line 2
Cheers
Harwinder

[Vad Fogel]

It doesn't compile for me with the following listing:

OuterReferVarOfStaticInner.java [7:1] qualified new of static class
        int j= tt.new StaticInner().i; //error line 1         
                  ^
1 error
Errors compiling OuterReferVarOfStaticInner.

I'm using JDK 1.4.2. And you guys?

[Harwinder Bhatia]

Ok, I admit, I'm using an older version 1.2.2. That's all I got at work. But I've got 1.4.2 installed on my PC at home and will go back and verify the results in a few hrs.
But I trust Cathy & Vad on that.
Cheers
Harwinder

[Dan Gun]

JDK 1.4.1 came up with this compiling error:
"Illegal enclosing instance specification for type OuterReferVarOfStaticInner.StaticInner"

[Chris Allen]

Originally posted by Cathy Song:

 
    public class OuterReferVarOfStaticInner {
       static class StaticInner {
         static int i=100;
      }
      
       public static void main(String[] args) {
         OuterReferVarOfStaticInner tt = new OuterReferVarOfStaticInner();
         //int j= tt.new StaticInner().i; //error line 1
         int j = OuterReferVarOfStaticInner.StaticInner.i; //line 2 ok
         System.out.println(j);
      }
   }

Why does line 1 not compile?
Thanks.

When referring to a static class whether it be top level or nested, you cannot use an instance variable to get to it. For example, if you want to use a method from the Math class, you simply use Math.<method name>. You do not instantiate a static class. Same rule applies here even though it is nested. Use the fully-qualified class name to refer to the variable in the static class: OuterReferVarOfStaticInner.StaticInner.i

[Cathy Song]

Hi Chris,
Math class is NOT static. And top-level classes MAY NOT be static. The reason you cant create an instance of Math is because its constructor is private.
You'll get the following error:
"Math() has private access in java.lang.Math"
The reason you can access the methods of Math class without creating an instance of Math is because the *methods* are static, that means thay are NOT associated with an instance of the class, rather the class itself. That is why static methods are also called class methods.

Thanks.

[Harwinder Bhatia]

With Java 1.4.2_02, I get the same error message as Vad mentioned above.
Btw, you could use:
int j = new OuterReferVarOfStaticInner.StaticInner().i; //line 3 ok
OR
int j = new StaticInner().i; //line 4 ok
Cheers
Harwinder
[ November 12, 2003: Message edited by: Harwinder Bhatia ]

[Alton Hernandez]

For a static member class, you don not use the instance of the enclosing class to access it.

[Harwinder Bhatia]

All I have read is that for a static nested class, you don't need an instance of the enclosing class. But, I've "not" read anywhere that you absolutely 'cannot' (compile-time error) specify an instance of the outer class.
Could somebody please clarify?
Thanks
Harwinder

[pallavi pandey]

The static nested class is tied only to the outer class, not an instance of the outer class.

[Jose Botella]

Welcome to the Ranch Pallavi, Chris and Dan.
__________________________________________________________________
This is from JLS 15.9

ClassInstanceCreationExpression:
new ClassOrInterfaceType ( ArgumentListopt ) ClassBodyopt
Primary.new Identifier ( ArgumentListopt ) ClassBodyopt
Class instance creation expressions have two forms:
* Unqualified class instance creation expressions begin with the keyword new. An unqualified class instance creation expression may be used to create an instance of a class, regardless of whether the class is a top-level (�7.6), member (�8.5, �9.5), local (�14.3) or anonymous class (�15.9.5).
* Qualified class instance creation expressions begin with a Primary. A qualified class instance creation expression enables the creation of instances of inner member classes and their anonymous subclasses.

And from JLS 15.9.1

Otherwise, the class instance creation expression is a qualified class instance creation expression. It is a compile-time error if Identifier is not the simple name (�6.2) of an accessible (�6.6) non-abstract inner class (�8.1.2) T that is a member of the compile-time type of the Primary. It is also a compile-time error if Identifier is ambiguous (�8.5). The class being instantiated is the class denoted by Identifier.

Thus it seems that the compiler is getting more and more JLS compliant.
[ November 12, 2003: Message edited by: Jose Botella ]