Comparing two Collections for "equality"

[Gavin Bong]

I have two Collections A and B. Both contain the same object types.
I want to compare both Collection for equality. This is how I am
doing it now. Pseudocode follows:

  public static boolean equal(Collection a, Collection b){
      if (a == null || b == null)
          throw new IllegalArgumentException("boo");
      if (a.size() != b.size())
          return false;
      if (a.containsAll(b) && b.containsAll(a))
          return true;
      return false;
  }

Does anybody see any holes in the logic / code above ?
Thanks all
Gavin

[Jeanne Boyarsky]

You are assuming that all the objects have an equals method defined? (this assumption is ok, I just want to state it.)
You may run into trouble if the collections contain duplicates. For example if collection a is [X,X,Y] and collection b is [X,Y,Y], your code will not catch the difference.
If the collections can't contain duplicates, the second check for containsAll is redundant.

[Gavin Bong]

Jeanne,
Thanks for your observations.
The parameters "can" and "may" contain duplicates.
I wonder whether I can just simplify it by doing

Collection a = ...
Collection b = ...
a.equals(b);

Gavin
[ October 01, 2003: Message edited by: Gavin Bong ]