Limiting creation of an object by a single class

[Gaurav Gupta]

Hi,
I have a class A and a class B.
Now - can I do an enforcement which says that only B (and no other class) should be able to create objects of class A?
thanks,
Gaurav

[Ben Dover]

Your problem is very similar to the singleton pattern, except for a nested class. Try this:

 class B {
   static A getA() {
      return new A();
   }
   // private nested class
   static class A {
      private A() {
         // constructor can only be called by A or B
      }
      public void hello() {
         System.out.println("hello from new A");
      }
   }
}
class Test {
   public static void main(String[] args) {
      B.A a; // a = new A() would be illegal because 
             // A's constructor is priv.
      a = B.getA();
      a.hello();
   }
}