java.util · java.base · since Java 1.2

TreeMap

declaration

public class TreeMap<K, V> extends AbstractMap<K, V>
        implements NavigableMap<K, V>, Cloneable, Serializable

Red-black-tree map with keys always sorted: O(log n) operations plus NavigableMap nearest-key and range queries hashes cannot answer.

Key methods

`K firstKey() / K lastKey()`	Extremes among keys — throws NoSuchElementException if empty.
`Map.Entry<K,V> firstEntry() / lastEntry()`	Extremes as entries — null-returning, not throwing.
`K floorKey(K) / ceilingKey(K)`	Nearest ≤ / ≥ key, or null.
`K lowerKey(K) / higherKey(K)`	Nearest strictly < / > key, or null.
`Map.Entry<K,V> floorEntry(K) / ceilingEntry(K)`	Nearest ≤ / ≥ entries.
`Map.Entry<K,V> pollFirstEntry() / pollLastEntry()`	Retrieve-and-remove the extreme entries.
`NavigableMap<K,V> headMap/tailMap/subMap(…)`	Range views over the sort order, live and write-through; boolean flags control endpoint inclusion.
`NavigableMap<K,V> descendingMap()`	Reverse-order view backed by the same tree.