Re: New functionality in the Set<T> interface.(was: TreeSet and HashSet)

"Daniel Pitts" <>
2 Feb 2007 12:00:07 -0800
On Feb 2, 11:40 am, "Marcin" <> wrote:


There is a very useful functionality, that I think should be implemented in
TreeSet nad HashSet
that is the method: Object get(Object o).
The method should return the same object from colletion as the parameter
In TreeSet complexity would be log(n), in HashSet would be constant.
With lack of this functionality one must implement collections on maps, so
the unnecessary and more complex type will be used.

What do you think about this?


What would be the use case of this?
would it return null if the set didn't contain the object o?
Also, this should be in the Set interface, if anywhere.

Whats so hard about using boolean contains(Object o)?

Or, are you basically using a Set<SomeTypeThatHasBothKeyAndValue>?
In that case, you SHOULD use a Map. Thats the whole point on maps, is
that you can key on the value.

If you want to have an AssociativeSet<T>, thats something a little
different than a standard Set

class AssociativeSet<T> implements Set<T> {
    final Map<T, T> associations;
    public AssociativeSet() {
       associations = new HashMat<T, T>();

    public AssociativeSet(Map<T, T> backingMap) {
       associations = backingMap;

    public T get(T o) {
      return associations.get(o);
    // TODO: delegate most of the Set methods to associations keySet

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