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Java / Map and its implementations

How do you sort a TreeMap by comparing its value?

You can't have the TreeMap itself sort on the values, since that defies the SortedMap specification, "A Map that further provides a total ordering on its keys". However, using an external collection, you can always sort Map.entrySet() either by key, values, or other sorting as needed.

package net.javapedia.algorithms;

import java.util.*;
import java.util.stream.Collectors;

public class SortMapByValueForlowestToHighest {

    public static void main(String[] args) {
        usingLinkedHashMap();
    }

    public static void usingLinkedHashMap() {
            Map<String, Integer> monthToExpense = new HashMap<>();
            monthToExpense.put("Jan",3);
            monthToExpense.put("Feb",5);
            monthToExpense.put("Mar",1);
            monthToExpense.put("Apr",0);
            monthToExpense.put("May",11);
            System.out.println(monthToExpense);
            monthToExpense= monthToExpense.entrySet().stream().sorted(Map.Entry.comparingByValue()).collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (e1,e2)->e1, LinkedHashMap::new));
            System.out.println(monthToExpense);
    }

}

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Set and its implementations

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