Referencing an enclosing instance from an inner class

java

Solution

I know this is part of the Java spec, but exactly what is going on when you use .this?

It just refers to a "hidden" field within `Bar`. It's easiest to see this by decompiling. You'll see that there's a `Bar` constructor taking a reference to an instance of `Foo`. That reference is stored in a field, and then when you use `Foo.this`, it just accesses that field. So assuming you'd put your `Foo.this.doSomething()` into a `someMethod` call, your code is similar to:

class Foo {

   static class Bar {
      private final Foo $foo;

      Bar(Foo foo) {
          this.$foo = foo;
      }    

      public void someMethod() {
          $foo.doSomething();
      }
   }
}

Problem

This is a knowledge/curiosity question only. After several years in Java, this has only just struck me. ``` class Foo { class Bar{ Foo.this.doSomething(); } } ``` When I look at `Foo.this`, I would assume that it's a static reference which obviously is not the case. I know this is part of the Java spec, but exactly what is going on when you use `<Class>.this`? Is it one of those "it just is" things?

Original source