TreeSet : Java Glossary

With TreeSets the key must be embedded in the object you store in the collection. Often you might have TreeSet of Strings. All you can do then is tell if a given String is in the Set. It won’t find you an associated object he way a Treemap will. With a TreeMap the keys and the objects they are associated with are separate.

TreeSet and its brother TreeMap oddly have nothing to do with representing trees. Internally they use a tree organisation to give you an alphabetically sorted Set/Map, but you have no control over links between parents and children.

Internally TreeSet uses red-black trees. There is no need to presort the data to get a well-balanced tree. On the other hand, if the data are sorted (ascending or descending), it won’t hurt as it does with some other types of tree.

If you don’t supply a Comparator to define the ordering you want, TreeSet requires a Comparable implementation on the item class to define the natural order.

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