Name: mc57594 Date: 02/12/97


In Java 1.1, an instance of an inner class Inner may access it's
enclosing instance of class Outer by using the syntax
Outer.this

This syntax doesn't work if Inner is a subclass of
Outer. For example:

public class Outer {
  
  int foo() { return 1; }

  public class Inner extends Outer {
    int foo() { return Outer.this.foo(); }
  }

  Inner getInner() { return new Inner(); }

  public static void main(String[] args) {
    Outer x = new Outer();
    Outer.Inner y = x.getInner();
    System.out.println(y.foo());
  }
}

Class Inner is a subclass of Outer, and overrides Outer.foo().
The intent is for Inner.foo() to call the foo() of it's
enclosing instance. However, because Inner is a subclass of
Outer, "Outer.this" is just a synonym for "this." The
result is, instead of calling the enclosing instance's foo()
this.foo() is called: instead of returning the value 1,
the program is caught in an infinite loop.

There are at least two possible solutions to this problem:
a) Never allow an inner class to be a subclass of an outer class.
If you want to achieve the effect desired above, you must write
a top-level subclass of Outer.

b) Provide a keyword, e.g. "enclosing", which is always a
reference to the enclosing instance. In this case, Inner.foo()
could be written as:

int foo() { return enclosing.foo(); }
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