Limit access on returned Collection

Question

Hello, is it possible to write a method to return a collection and don't allow the caller to add or remove objects from the collection, but allow the caller modify the objects in the collection.

Answer 1

Hello, is it possible to write a method to return a
collection and don't allow the caller to add or remove
objects from the collection, but allow the caller
modify the objects in the collection.Well there is nothing to stop someone from modifying the object in a Collection other than through that Collection itself.
Do you mean you want to allow people to replace immutable objects like Strings but not add or remove them?
The only Collections this would seem to make any sense for are Lists. YOu ca nso this pretty easily. extend AbstractList and implement the get(index) and size methods. Then implement the set(index. object) method so that it throws an exception if the index >= size.
Oh here it is:
UpdateableList extends AbstractList {
   List list;
   public UpdateableList(List list) {
      if (list == null)  throw new IllegalArgumentException();
      this.list = list;
   public Object get(int index) {
      return list.get(index);
   public int size() {
      return list.size();
   public Object set(int index, Object object) {
      if (index >= size) throw new IndexOutOfBoundsException();
      return list.set(index, object);
}Note, I'm not sure but allowing the set method may open up the add other methods, so you might need to throw UnsupportedOperationException in those methods.