Why are "static final" fields allowed in inner classes?

Question

I have a doubt in using Inner Classes in java. Here is my code.

Code:

public class Test{

      public class InnerClass{
             public static int num = 10;
      }       

}

It's not allowed. I got the error message "The field num cannot be declared static; static fields can only be declared in static or top level types".

public class Test{

      public class InnerClass{
             public static final int num = 10;
      }       

}

But It's allowed. I have not declared InnerClass as static and top level element but how it works?

Doesn't the error tell you the answer? If the class is static or if it is top level, it is allowed. — Karthik T, Feb 07 '13 at 05:41
This question is taking it a step further to ask why a constant (`static final`) field is allowed. — Paul Bellora, Feb 07 '13 at 05:51
@KarthikT , Please read my question. I am asking why constant fields are allowed in inner class? — kannanrbk, Feb 07 '13 at 05:52
@bharathi Sorry my miss-understanding, will vote to reopen if it gets closed.. — Karthik T, Feb 07 '13 at 05:56
Actually this question is also semi-addressed in the other answer: only "compile-time constant fields" are allowed to be `static final` in this context. (Of course, one could ask _why_ that was decided. I guess convenience?) — Stephan202, Feb 07 '13 at 05:58

Karthik T · Answer 1 · 2013-02-07T06:08:18.143

8

To quote from the linked answer.

8.1.2 Inner Classes and Enclosing Instances
...
Inner classes may not declare static members, unless they are compile-time constant fields (§15.28).

final makes them constant once initialized, = 10 is a compile time constant value. Thus it is allowed.

edited Feb 07 '13 at 06:08

answered Feb 07 '13 at 05:58

Karthik T

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Why are "static final" fields allowed in inner classes?

1 Answers1