TreeSet类 : 树集 « 集合 « Java 教程

1. The other concrete Set implementation is the TreeSet.
2. A TreeSet keeps its elements ordered internally.
3. The tree is balanced, it's a red-black tree.
4. Having a balanced tree guarantees a quick o(log n) search time at the cost of a more time-intensive insertion (and deletion).
5. Elements added to the tree must be orderable.

Red-black tree rules refresher:

1. Every node in the tree is either black or red.
2. The root is always black.
3. If a node is red, its children must be black.
4. Every path from the root to a leaf (or null child) must contain the same number of black nodes. (referenced from "Java Collections by John Zukowski Apress 2001")