Comments on: Instantiating Java inner-class objects, from a different class.

By: New Adventures in Software » More Stupid Java Tricks

New Adventures in Software » More Stupid Java Tricks — Tue, 26 Aug 2008 19:00:32 +0000

[...] but they don’t necessarily have to be instantiated within the scope of the parent class. Daniel Pitts shows another way. File this one under “ugly syntax” and “surely that’s not supposed to [...]

By: Daniel

Daniel — Fri, 07 Dec 2007 15:29:27 +0000

I think you can edit comments if you’re logged in when you comment. Also, you can use

to denote code snippets on this site :-).

Thanks for the comment.

By: Piotr Kobzda

Piotr Kobzda — Fri, 07 Dec 2007 14:45:02 +0000

Daniel, in my previous comment submission here, I used a tag around my example, but it doesn’t looks so nice rendered on a page. So, my message needs some formatting (maybe also my English correction?) before publishing (of course, if you think it’s worth of that…). Possibly adding a

 tag around the code is enough… but I’m sure you can correct it the better way… 

Also, now I think that my example could be a bit nicer with all occurrences of “outer” replaced with “get” — of course, it works without that change as well.  
TIA for correcting me! :-))
BTW, it would be a nice feature of your web-site, to be able to correct/remove own postings before your acceptation.
P.S. This message is not an article comment, and you can freely remove it.
P.S.2 Nice site!



By: Piotr Kobzda
Piotr Kobzda — Fri, 07 Dec 2007 12:07:16 +0000
Other, not obvious IMHO, but also interesting (and even more “esoteric” I think) feature of Java, is an ability of a single instance of inner class to have multiple (and different!) enclosing class’ instances.
An example:
class EnclosingInstancesTest {
  public static void main(String... _) {
     A a = new A();
     A.I ai = a.new I();
     assert(ai.outerA()==a);

     B b = new B();
     B.I bi1 = b.new I();
     assert(bi1.outerA()==b && bi1.outerB()==b);
     B.I bi2 = b.new I(a);
     assert(bi2.outerA()==a && bi2.outerB()==b);
  }
}

class A {
  class I {
    A outerA() { return A.this; }
  }
}

class B extends A {
  class I extends A.I {
    I() { }
    I(A a) { a.super(); }
    B outerB() { return B.this; }
  }
}

I don’t really know any important usage of that feature, but I hope it’s worth to know about it.