LinkedHashSet - insertion order and duplicates - keep newest "on top"

Question

I need a collection that keeps insertion order and has unique values. LinkedHashSet looks like the way to go, but there's one problem - when two items are equal, it removes the newest one (which makes sense), here's an example:

set.add("one");
set.add("two");
set.add("three");
set.add("two");

The LinkedHashSet will print:

one, two, three

But what I need is:

one, three, two

What would be the best solution here? Is there any collection/collections method that can do this or should I implement it manually?

Answer 1

Most of the Java Collections can be extended for tweaking.

Subclass LinkedHashSet, overriding the add method.

class TweakedHashSet<T> extends LinkedHashSet<T> {

    @Override
    public boolean add(T e) {
        // Get rid of old one.
        boolean wasThere = remove(e);
        // Add it.
        super.add(e);
        // Contract is "true if this set did not already contain the specified element"
        return !wasThere;
    }

}