Static nested classes in Java

Question

I'm unsure why this code compiles... quoting the Java tutorials:

like static class methods, a static nested class cannot refer directly to instance variables or methods defined in its enclosing class — it can use them only through an object reference.

Src: http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html

public class StaticNested {

    private String member;
    private static String staticMember;

    static class StaticNestedClass {
        private void myMethod() {
            System.out.println(staticMember);
            StaticNested nested = new StaticNested();
            System.out.println(nested.member);
        }
    }
}

I didn't expect to be able to access member directly, but the code compiles fine. Am I misunderstanding the Java spec?

Sorry about the formatting, I'm struggling with my browser + post editor.

Oliver Charlesworth · Accepted Answer · 2013-01-16 02:17:37Z

8

You aren't accessing instance members directly.

staticMember is accessing a non-instance member, and nested.member is accessing one through an object reference.

answered Jan 16, 2013 at 2:17

Oliver Charlesworth

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2 Comments

cjtightpant Over a year ago

What I'm curious about was that I can access nested.member without an accessor method...inner classes can access directly private members of the outer class I suppose...

Oliver Charlesworth Over a year ago

@cjtightpant: Yes, that's true.

Pshemo · Accepted Answer · 2013-01-16 02:22:37Z

2

It is correct behavior. What spec meant is that (in your code example) you cant access non-static member field String member directly in static nested class like

public class StaticNested {

    private String member;
    private static String staticMember;

    static class StaticNestedClass {
        private void myMethod() {
            System.out.println(staticMember);
            System.out.println(member);//<-here you will get compilation error
        }
    }
}

but because non-static fields belongs to object of class you can access it with reference to that object like in your code

StaticNested nested = new StaticNested();
System.out.println(nested.member);

answered Jan 16, 2013 at 2:22

Pshemo

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Comments

Bohemian · Accepted Answer · 2013-01-16 02:41:59Z

1

You are accessing it via an instance (not statically).

This does not compile:

System.out.println(member);

Compiler message:

Cannot make a static reference to the non-static field member

edited Jan 16, 2013 at 2:41

answered Jan 16, 2013 at 2:28

Bohemian♦

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