What is NavigableMap in Java 6 - Creating subMap from Map with Example

NavigableMap in Java 6 is an extension of SortedMap  like TreeMap
which provides convenient navigation method like lowerKey, floorKey, ceilingKey and higherKey. NavigableMap is added
on Java 1.6 and along with these popular navigation method it also provide ways
to create a Sub Map from existing Map in
Java e.g. headMap whose keys are less than
specified key, tailMap whose keys are greater than
specified key and a subMap which is strictly contains keys
which falls between toKey and fromKey. All of
these methods also provides a boolean to include specified key or not. TreeMap
and ConcurrentSkipListMap are two concrete implementation of NavigableMap in Java
1.6 API. Though NavigableMap is not as popular as HashMap,
ConcurrentHashMap
or Hashtable
but given that TreeMap implements NavigableMap you
already get all good things in a well known Map implementation.

How to use
NavigableMap in Java - Example

In this Java tutorial we will explore some API methods of NavigableMap to show
its functionality. This Java program shows example of lowerKey which
returns keys less than specified, floorKey returns
key less than or equal to, ceilingKey return
greater than or equal to and higherKey which
returns keys which are greater than specified key. This Java example also
demonstrate use of headMap(), tailMap() and subMap() method
which is used to create Map from an
existing Map in Java. headMap returns a Map
whose keys are lower than specified keys while tailMap returns
Map which contains keys, those are higher than specified. Here is complete code
example of How to use NavigableMap in
Java.

import java.util.NavigableMap;

import java.util.TreeMap;



/**

 *

 * Java program to demonstrate What is NavigableMap in Java and How to
use NavigableMap

 * in Java.
NavigableMap provides two important features navigation methods

 * like
lowerKey(), floorKey, ceilingKey() and higherKey().

 * There Entry counterpart and methods to create subMap e.g. headMap(),
tailMap()

 * and
subMap().

 *

 * @author Javin Paul

 */

public class
NavigableMapExample {



    public static void
main(String args[]) {

     

        //NavigableMap
extends SortedMap to provide useful navigation methods

        NavigableMap<String,
String> navigableMap = new TreeMap<String,
String>();

     

        navigableMap.put("C++", "Good programming language");

        navigableMap.put("Java",
"Another good programming language");

        navigableMap.put("Scala",
"Another JVM language");

        navigableMap.put("Python",
"Language which Google use");

     

        System.out.println("SorteMap : " + navigableMap);

     

        //lowerKey returns
key which is less than specified key

        System.out.println("lowerKey from Java : " + navigableMap.lowerKey("Java"));

     

        //floorKey returns
key which is less than or equal to specified key

        System.out.println("floorKey from Java: " + navigableMap.floorKey("Java"));

     

        //ceilingKey returns
key which is greater than or equal to specified key

        System.out.println("ceilingKey from Java: " + navigableMap.ceilingKey("Java"));

     

        //higherKey returns
key which is greater specified key

        System.out.println("higherKey from Java: " + navigableMap.higherKey("Java"));

     

     

        //Apart from
navigagtion methodk, it also provides useful method

        //to create subMap
from existing Map e.g. tailMap, headMap and subMap

     

        //an example of
headMap - returns NavigableMap whose key is less than specified

        NavigableMap<String,
String> headMap = navigableMap.headMap("Python", false);

        System.out.println("headMap created form navigableMap : " +
headMap);

             

        //an example of
tailMap - returns NavigableMap whose key is greater than specified

        NavigableMap<String,
String> tailMap = navigableMap.tailMap("Scala", false);

        System.out.println("tailMap created form navigableMap : " +
tailMap);

     

        //an example of
subMap - return NavigableMap from toKey to fromKey

        NavigableMap<String,
String> subMap = navigableMap.subMap("C++", false
,

                                                                  "Python", false);

        System.out.println("subMap created form navigableMap : " +
subMap);

    }

}



Output:

SorteMap : {C++=Good
programming language, Java=Another good programming language, Python=Language
which Google use, Scala=Another JVM language}

lowerKey from Java : C++

floorKey from Java: Java

ceilingKey from Java: Java

higherKey from Java: Python

headMap created form navigableMap : {C++=Good programming language, Java=Another good programming
language}

tailMap created form navigableMap : {}

subMap created form navigableMap : {Java=Another good programming language}

That's all on What is NavigableMap in Java and How to use NavigableMap with
example. We have seen examples of popular navigation method on TreeMap e.g. floorKey. You can
also use similar method like lowerEntry, floorEntry, ceilingEntry and higherEntry to retrieve
Entry instead of key. NavigableMap is also a good utility to create
subset of a Map in Java.

Other Java Collection tutorials from Javarevisited blog

How
to sort HashMap in Java by keys and values

4
ways to traverse Map in Java with Example

How
to compare two Arrays in Java using Equals and deepEquals

3
ways to print value of element of an Array in Java

How
to remove duplicate elements from ArrayList in Java

Source:http://javarevisited.blogspot.com/2013/01/what-is-navigablemap-in-java-6-example-submap-head-tail.html