getting a copy of an object

[imran quazi]

Hi,

I have this code:

  
ArrayList a1 = new ArrayList();
ArrayList a2 = new ArrayList();
 
 a1.add("1");
 a1.add("2");
 a1.add("3");
  

Now I want a copy of a1 assigned to a2, but the original a1 will not be affected, so if I remove an element from a2, from a1 it won't remove.

I don't want to use clone. Is there any way to do that?

Kindly help.

Advance thanks, imran

[David O'Meara]

The API is your friend:

a2.addAll(a1)

[imran quazi]

Thanks a lot David,
I was doing the same thing, i.e, iterating the 1st array and putting the value in the 2nd one. this method does it more neatly.

BTW, this is ok for arrays, but what if its not an array? then is it possible to do what i asked for?

[David O'Meara]

addAll is defined by the Collection interface, so it is supported by any concrete Class that implements this interface.

[Jim Yingst]

Well, to be fair, the Collection interface lists the method as optional. It can throw an UnsupportedOperationException in some cases. So in truth, there is no general answer to Imran's last question; it depends on the specific Collection implementation that we are talking about. Most collections implement this method, but a few, like the implementations returned by Collections.unmodifiableXXX() and Arrays.asList(), do not. The idea of optional methods in an interface is a bit odd, and in Java I think it's unique to the collections framework. Generally an interface promises that a method will be available in an implementing class. But with an optional method, the promise is that the method will be present in the class, but it may throw an exception. So the method is available, except that it really isn't.