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

Answer 1

Most of the Java Collections can be extended for tweaking.

Subclass LinkedHashSet, overriding the add method.

class TweakedHashSet extends LinkedHashSet {

    @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;
    }

}