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

Wednesday, 4 February 2015

Java : Collection Framework : TreeMap (decendingMap)

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TreeMapExample.java

import java.util.NavigableMap;
import java.util.Set;
import java.util.TreeMap;

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

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

        treeMap.put(10, "Cat");
        treeMap.put(40, "Dog");
        treeMap.put(30, "Apple");
        treeMap.put(20, "Ball");
        
        System.out.println("treeMap : " + treeMap + "\n");

        /*
         * Returns a reverse order NavigableSet view of the keys contained in
         * this map. The set's iterator returns the keys in descending order.
         * The set is backed by the map, so changes to the map are reflected in
         * the set, and vice-versa.
         * 
         * If the map is modified while an iteration over the set is in progress
         * (except through the iterator's own remove operation), the results of
         * the iteration are undefined. The set supports element removal, which
         * removes the corresponding mapping from the map, via the
         * Iterator.remove, Set.remove, removeAll, retainAll, and clear
         * operations. It does not support the add or addAll operations.
         */
        NavigableMap<Integer,String> NavigableMap = treeMap.descendingMap();

        System.out.println("NavigableMap : " + NavigableMap + "\n");
        
        Set<Integer> set = NavigableMap.keySet();

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

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

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

        }

    
    }
}

Output

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

NavigableMap : {40=Dog, 30=Apple, 20=Ball, 10=Cat}

set : [40, 30, 20, 10]

-----------------------
Key | value
-----------------------
40   |  Dog
30   |  Apple
20   |  Ball
10   |  Cat