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From: markspace <-@.>
Newsgroups: comp.lang.java.programmer
Subject: Re: Automatic linking of related objects in constructor
Date: Wed, 29 Jun 2011 09:17:29 -0700
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On 6/29/2011 2:56 AM, Qu0ll wrote:
> Suppose you have class A which contains a list of objects of class B and
> that the constructor for B takes in a reference to the A object which is
> to include it in said list. Is it safe to make a call to A's method
> addB(B b) in that B constructor passing in "this"? I have heard that
> it's bad practice to "leak" a reference to an object from within its own
> constructor because it may be in an invalid state.


Yes, imo this is correct.  It seems that sometimes you have to do it 
(constructing Swing components) but in general it's a bad idea.


> If not, how else can I automatically add the B object to the list in A
> without forcing the client programmer to explicitly call addB() given
> that they have already passed in the B as an argument?


I like the factory pattern best here

class A {

   private ArrayList<B> list;

   private A() {}

   /** Factory for constructing new A's */
   public static A newInstance( B... bs ) {
     A a = new A();
     a.list = new ArrayList<B>();
     a.list.addAll( bs );
     return a;
   }
}