Tutorials : Parsing with StAX in JDK 6.0 :

NavigableMap

Order methods	Polls methods	LHCF methods	Submap methods
descendingMap	firstEntry	lowerEntry	headMap
descendingKeySet	lastEntry	lowerKey	subMap
	pollFirstEntry	higherEntry	tailMap
	pollLastEntry	higherKey
		ceilingEntry
		ceilingKey
		floorEntry
		floorKey

Table 1. The NavigableMap is an interface that provides methods dedicated to access entries of an SortedMap.

Let's go through these items:

• Order methods are used for create descending views of a SortedMap.
  • public NavigableMap descendingMap() obtains a reverse order view of the current map.
  • public NavigableSet descendingKeySet() obtains a reverse order navigable set view of the keys in the current map.

  Note: In both cases, the changes to the map are reflected in the descending result and vice-versa.

  Listing 7 shows you how to create a NavigableMap and how to use the descendingKeySet method—in the same manner you can use the descendingMap method.

• Polls methods are used to extract elements from a SortedMap.
  • public java.util.Map.Entry firstEntry() returns the entry with the least key from the current SortedMap.
  • public java.util.Map.Entry lastEntry() returns the entry with the greatest key from the current SortedMap.
  • public java.util.Map.Entry pollFirstEntry() removes and returns the entry with the least key from the current SortedMap.
  • public java.util.Map.Entry pollLastEntry() removes and returns the entry with the greatest key from the current SortedMap.

  Listing 8 demonstrates how to use the above methods. Figure 7 shows a graphical view of the application shown in Listing 8.




• LHCF methods include the lowerKey/lowerEntry (L), higherKey/higherEntry (H), ceilingKey/ ceilingEntry (C) and floorKey/floorEntry (F) methods.
  • public java.lang.Object lowerKey(java.lang.Object key) returns the greatest key "<" than the given key (null if there is no such key).
  • public java.lang.Object higherKey(java.lang.Object key) returns the least key ">" than the given key (null if there is no such key).
  • public java.lang.Object ceilingKey(java.lang.Object key) returns the least key ">=" to the given key (null if there is no such key).
  • public java.lang.Object floorKey(java.lang.Object key) returns the greatest key "<=" to the given key (null if there is no such key).

  The lowerEntry, higherEntry, ceilingEntry, and floorEntry are similar to the above corespondents, but they are used for entries.

  Listing 9 shows an example of how to use the above XXXKey methods (the tested key was "9.0"). Figure 8 shows a graphical view of the application in Listing 9.

  
  

  Listing 10 is an example of using the above XXXEntry methods (the key of the tested entry was "9.0"). Figure 9 shows a graphical view of the application in Listing 10.




• Subset methods used to extract a submap from a SortedMap.
  • public NavigableMap headMap(java.lang.Object toKey,boolean inclusive) returns a submap-view of the current map whose keys are less than (or equal to, if inclusive is true) toKey. Another headMap method is: public java.util.SortedMap headMap(java.lang.Object toKey).
  • public NavigableMap subMap(java.lang.Object fromKey, boolean fromInclusive, java.lang.Object toKey, boolean toInclusive) returns a submap-view of the current map whose keys range is [fromKey,toKey). By modifying the fromInclusive and toInclusive arguments you can obtain the following ranges: [fromKey,toKey], (fromKey,toKey), and (fromKey,toKey]. Another subMap method is: public java.util.SortedMap subMap(java.lang.Object fromKey,java.lang.Object toKey).
  • public NavigableMap tailMap(java.lang.Object fromKey,boolean inclusive) returns a submap-view of this map whose keys are greater than (or equal to, if inclusive is true) fromKey. Another tailMap method is: public java.util.SortedMap tailMap(java.lang.Object fromKey).

  In all cases, the returned submap is backed by the current map, so changes in the returned submap are reflected in this map, and vice-versa.

  Listing 11 demonstrates how to use these methods. Figure 10 shows a graphical view of the application in Listing 11.

Food for Thought

So the question is: "Why weren't java.util.NavigableSet and java.util.NavigableMap implemented at the same time as SortedSet and SortedMap?"

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