accessing outer class variables via an inner class reference

Question

 public static class Outer {
        public int field;
        public class Inner {}
 }


 //  caller methods
 public static void foo(Outer.Inner inner) {
       // here I want to access the "field"
       // tried the following, none worked
       System.out.println(inner.Outer.field);
       System.out.println(inner.Outer.this.field);
 }

How do I access a non-static fields of a class from a reference of its non-static inner class in Java?

P.S
People kept saying it's bad design. Yes, I agree 100% this is bad "design". At least, it's bad for code that needs to be read by humans. But if this is for generated code, I think I'll get a pass. (have anyone tried reading code that comes out of Antlr, for eg?)

Not a Java expert but that seems like an invalid thing to do. Why do you want to do this anyways, kind of sounds like an XY problem. — Andrew Li, Dec 15 '17 at 23:02
Nope you cant do that. You would have to add either getters to Outer or Inner — Antoniossss, Dec 15 '17 at 23:03
Look, I agree 100% this is bad "design". At least, it's bad for code that needs to be read by humans. But if this is for generated code, I think I'll get a pass. (have anyone tried reading code that comes out of Antlr, for eg?) — One Two Three, Dec 15 '17 at 23:29
Possible duplicate of [Getting hold of the outer class object from the inner class object](https://stackoverflow.com/questions/1816458/getting-hold-of-the-outer-class-object-from-the-inner-class-object) — Silvio Mayolo, Dec 15 '17 at 23:38

score 0 · Answer 1 · answered Dec 15 '17 at 23:04

Seems like a not-too-good idea, but anyway, you'll need to explicitly export it yourself.

public static class Outer {
    public int field;
    public class Inner {
        public Outer outer() {
            return Outer.this;
        }
    }
}

//  caller methods
public static void foo(Outer.Inner inner) {
   System.out.println(inner.outer().field);
}

score 0 · Answer 2 · answered Dec 15 '17 at 23:04

0

This could work - bad coding practice anyway

 public static class Outer {
        public int field;
        public class Inner {
            public Outer outer=Outer.this
        }
 }


 //  caller methods
 public static void foo(Outer.Inner inner) {
       System.out.println(inner.Outer.field);
       System.out.println(inner.Outer.this.field);
 }

answered Dec 15 '17 at 23:04

Antoniossss

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Ok, so essentially you expose a reference to the outer class. This feels like soemthing java should have made default! Thanks! – One Two Three Dec 15 '17 at 23:12
IMHO this is something you should rather avoid and redesign into simpler composition of classes. – Antoniossss Dec 16 '17 at 00:20

score 0 · Answer 3 · answered Dec 15 '17 at 23:12

One option is mentioned in the other answers. If for some reason it doesn't fit your case, you can expose field from Inner, with getter (and setter if you need to):

public Outer class {
    private int field;
    public class Inner {
        public int getOuterField() {
            return field;
        }
    }
}

A different approach would to be pass the corresponding Outer instance wherever you need to use Inner, so foo will take two arguments in this case.

And yeah, I agree with all the comments posted - all of the options indicate bad design.

accessing outer class variables via an inner class reference

3 Answers3