NavigableMap estends SortedMap with navigation methods.

Important properties of NavigableMap

1. Methods lowerEntry, floorEntry, ceilingEntry, and higherEntry return Map.Entry objects associated with keys respectively less than, less than or equal, greater than or equal, and greater than a given key, returning null if there is no such key.

   • Similarly, methods lowerKey, floorKey, ceilingKey, and higherKey return only the associated keys.

2. A NavigableMap may be accessed and traversed in either ascending or descending key order.

   • The descendingMap method returns a view of the map with the senses of all relational and directional methods inverted.

   • The performance of ascending operations and views is likely to be faster than that of descending ones.

3. Methods subMap, headMap, and tailMap differ from the like-named SortedMap methods in accepting additional arguments describing whether lower and upper bounds are inclusive versus exclusive.

4. This interface additionally defines methods firstEntry, pollFirstEntry, lastEntry, and pollLastEntry that return and/or remove the least and greatest mappings, if any exist, else returning null.

5. Implementations of entry-returning methods are expected to return Map.Entry pairs representing snapshots of mappings at the time they were produced.

   • However, it is possible to change mappings in the associated map using method put.

6. Methods subMap(K, K), headMap(K), and tailMap(K) are specified to return SortedMap to allow existing implementations of SortedMap to be compatibly retrofitted to implement NavigableMap,

   • but extensions and implementations of this interface are encouraged to override these methods to return NavigableMap.

   • Similarly, SortedMap.keySet() can be overriden to return NavigableSet.

Important methods of NavigableMap Interface

• ceilingEntry(K key)

  • Returns a Map.Entry with the least key greater than or equal to the given key, or null if there is no such key.

• ceilingKey(K key)

  • Returns the least key greater than or equal to the given key, or null if there is no such key.

• descendingKeySet()

  • Returns a reverse order NavigableSet view.

• descendingMap()

  • Returns a reverse order NavigableMap view.

• firstEntry()

  • Returns a Map.Entry with the least key in this map, or null if the map is empty.

• floorEntry(K key)

  • Returns a Map.Entry with the greatest key less than or equal to the given key, or null if there is no such key.

• floorKey(K key)

  • Returns the greatest key less than or equal to the given key, or null if there is no such key.

• headMap(K toKey)

  • Returns a SortedMap view of this map with keys strictly less than toKey.

• headMap(K toKey, boolean inclusive)

  • Returns a NavigableMap view of this map with keys less than (or equal to, if inclusive is true) toKey.

• higherEntry(K key)

  • Returns a Map.Entry with the least key strictly greater than the given key, or null if there is no such key.

• higherKey(K key)

  • Returns the least key strictly greater than the given key, or null if there is no such key.

• lastEntry()

  • Returns a Map.Entry with the greatest key in this map, or null if the map is empty.

• lowerEntry(K key)

  • Returns a Map.Entry with the greatest key strictly less than the given key, or null if there is no such key.

• lowerKey(K key)

  • Returns the greatest key strictly less than the given key, or null if there is no such key.

• navigableKeySet()

  • Returns a NavigableSet view of the keys contained in this map.

• pollFirstEntry()

  • Removes and returns a Map.Entry with the least key in this map, or null if the map is empty.

• pollLastEntry()

  • Removes and returns a Map.Entry with the greatest key in this map, or null if the map is empty.

• subMap(K fromKey, boolean fromInclusive, K toKey, boolean toInclusive)

  • Returns a NavigableMap view of this map with keys range from fromKey to toKey.

• subMap(K fromKey, K toKey)

  • Returns a SortedMap view of this map with keys range from fromKey, inclusive, to toKey, exclusive.

• tailMap(K fromKey)

  • Returns a SortedMap view of this map with keys are greater than or equal to fromKey.

• tailMap(K fromKey, boolean inclusive)

  • Returns a NavigableMap view of the portion of this map whose keys are greater than (or equal to, if inclusive is true) fromKey.