Why can you not use an initializer block for a static variable in an inner class?

Question

why does java not allow static declarations with a static initialization block in a non-static inner class?

in the below code, outer2 will work and inner2 will not, despite doing the same thing. any ideas? i'm not looking for a workaround, i'm just trying to understand why java fails to do this.

public class WhyUNoStatic {
    public static final String outer1 = "snth";  // ok
    public static final String outer2;  // ok
    static
    {
        outer2 = "snth";
    }

    public class Inner {
        public static final String inner1 = "snth";  // still ok! 
        public static final String inner2;  // FAILURE TIME
        static
        {
            inner2 = "snth";
        }
    }
}

edit: note that inner1 will work fine. it's not that java prohibits static vars in inner classes, it just prohibits declarations of them.

Because inner classes cannot have `static` non final members, and `static { }` is a static member. Maybe? — Luiggi Mendoza, Sep 22 '15 at 19:46
Java prohibits non-constant variables in inner classes. `inner1` is a constant variable. `inner2` is not. — Sotirios Delimanolis, Sep 22 '15 at 20:51

score 2 · Answer 1 · edited Jun 20 '20 at 09:12

2

The JLS, Section 8.1.3, disallows this behavior.

It is a compile-time error if an inner class declares a static initializer (§8.7).

It is a compile-time error if an inner class declares a member that is explicitly or implicitly static, unless the member is a constant variable (§4.12.4).

You declared your static variables final in your inner class, which is ok, but the static initializer is prohibited there.

edited Jun 20 '20 at 09:12

Community

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1

answered Sep 22 '15 at 19:48

rgettman

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And as for the reason why, it probably would've complicated the already quite complicated initialisation sequence even more. – biziclop Sep 22 '15 at 19:49
yeah, that's what i'm trying to get at. why can the compiler not handle this? i'd love to see a code example to show why it's difficult for the compiler to deal with this... – acushner Sep 22 '15 at 21:39

score 2 · Answer 2 · answered Sep 22 '15 at 19:50

2

See JLS Chapter 8

Inner classes may not declare static initializers (§8.7) or member interfaces, or a compile-time error occurs.

You can declare a nested class instead

public static class Inner {...}

answered Sep 22 '15 at 19:50

Peter L

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Why can you not use an initializer block for a static variable in an inner class?

2 Answers2