SortHashMapByValue.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.TreeMap;


public class SortHashMap {
	public static ArrayList<Map.Entry<String, Integer>> sortHashMapByValueWithCollections(HashMap<String, Integer> map){
		ArrayList<Map.Entry<String, Integer>> al = new ArrayList<>(map.entrySet());
		Collections.sort(al, new Comparator<Map.Entry<String, Integer>>(){
			public int compare(Map.Entry<String, Integer> o1, Map.Entry<String, Integer> o2){
				Integer first = o1.getValue();
				Integer second = o2.getValue();
				return first.compareTo(second);
			}
		});
		return al;
	}
	
	public static TreeMap<String, Integer> sortHashMapByValueWithTreeMap(HashMap<String, Integer> map){
		TreeMap<String, Integer> treeMap = new TreeMap<>(new ValueComparator(map));
		treeMap.putAll(map);
		return treeMap;
	}
	
	public static void main(String[] args) {
		HashMap<String, Integer> map = new HashMap<>();
		map.put("c", 1);
		map.put("b", 2);
		map.put("a", 3);
		System.out.println(map);

		ArrayList<Map.Entry<String, Integer>> al = sortHashMapByValueWithCollections(map);
		System.out.println(al);
		
		TreeMap<String, Integer> treeMap = sortHashMapByValueWithTreeMap(map);
		System.out.println(treeMap);
	}

}

class ValueComparator implements Comparator<String>{
	Map<String, Integer> map;
	public ValueComparator(Map<String, Integer> map){
		this.map = map;
	}
	public int compare(String a, String b){
		if(map.get(a) >= map.get(b)) return 1;
		else return -1;
	}
}