JAVA EE: Java : Collection Framework : TreeMap (headMap)

Wednesday, 4 February 2015

Java : Collection Framework : TreeMap (headMap)

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TreeMapExample.java

import java.util.Set;
import java.util.SortedMap;
import java.util.TreeMap;

/*
 * Example of headMap(K toKey) method.
 */
public class TreeMapExample
{
    public static void main( String[] args )
    {

        TreeMap<Integer, String> treeMap = new TreeMap<Integer, String>();

        treeMap.put(10, "Cat");
        treeMap.put(50, "Dog");
        treeMap.put(30, "Apple");
        treeMap.put(40, "Ball");
        treeMap.put(20, "Eagle");

        System.out.println("treeMap : " + treeMap + "\n");

        /*
         * Returns a view of the portion of this map whose keys are strictly
         * less than toKey. The returned map is backed by this map, so changes
         * in the returned map are reflected in this map, and vice-versa. The
         * returned map supports all optional map operations that this map
         * supports.
         * 
         * Equivalent to headMap(toKey, false).
         */
        SortedMap<Integer, String> sortedMap = treeMap.headMap(40);

        System.out.println("sortedMap : " + sortedMap + "\n");

        Set<Integer> set = sortedMap.keySet();

        System.out.println("set : " + set + "\n");

        System.out.println("-----------------------");
        System.out.println("Key" + " | " + "value");
        System.out.println("-----------------------");

        for( Integer key : set )
        {
            String value = sortedMap.get(key);
            System.out.println(key + "   |  " + value);

        }

    }
}

Output

treeMap : {10=Cat, 20=Eagle, 30=Apple, 40=Ball, 50=Dog}

sortedMap : {10=Cat, 20=Eagle, 30=Apple}

set : [10, 20, 30]

-----------------------
Key | value
-----------------------
10   |  Cat
20   |  Eagle
30   |  Apple