How to sort HashMap in java by keys and values

Table of Contents

Java HashMap tutorial:
- - Sorting by Keys:
  - Sorting by values:
- Sorting by Keys example :
  - Sorting by values example:
  - Explanation:

HashMap does not preserve order of element but what if you want to sort it by keys or values. In this post, we will see how to sort HashMap by keys or values.

Java HashMap tutorial:

Sorting by Keys:

Sorting by keys can be easily done using TreeMap. You just need to pass HashMap to the constructor of TreeMap.


TreeMap map=new TreeMap(Map hm);

TreeMap map=new TreeMap(Map hm);

Sorting by values:

We can use Comparator to sort it by values.

Sorting by Keys example :

Create Country.java as below. It should implement Comparable interface


package org.arpit.java2blog;  
public class Country implements Comparable {  

 String name;  
 long population;  

 public Country(String name, long population) {  
  super();  
  this.name = name;  
  this.population = population;  
 }  
 public String getName() {  
  return name;  
 }  
 public void setName(String name) {  
  this.name = name;  
 }  
 public long getPopulation() {  
  return population;  
 }  
 public void setPopulation(long population) {  
  this.population = population;  
 }
@Override
public int compareTo(Object o) {
    Country country=(Country) o;
 return this.getName().compareTo(country.getName());
}  

}

package org.arpit.java2blog;

public class Country implements Comparable {

String name;

long population;

public Country(String name, long population) {

super();

this.name = name;

this.population = population;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

public long getPopulation() {

return population;

}

public void setPopulation(long population) {

this.population = population;

}

@Override

public int compareTo(Object o) {

Country country=(Country) o;

return this.getName().compareTo(country.getName());

}

Create TreeMapCompMain.java as below:


package org.arpit.java2blog;

import java.util.HashMap;
import java.util.Iterator;
import java.util.TreeMap;

public class TreeMapCompMain {

 public static void main(String[] args)
 {
  Country india=new Country("India",1000);  
        Country japan=new Country("Japan",10000);  

        Country france=new Country("France",2000);  
        Country russia=new Country("Russia",20000);  

        HashMap<country string> countryCapitalMap=new HashMap<country>();  
        countryCapitalMap.put(india,"Delhi");  
        countryCapitalMap.put(japan,"Tokyo");  
        countryCapitalMap.put(france,"Paris");  
        countryCapitalMap.put(russia,"Moscow");  

        System.out.println("Sorting HashMap by passing it to TreeMap constructor");
        TreeMap<country> sortedTreeMapCountryCapital=new  TreeMap<country> (countryCapitalMap);
        Iterator countryCapitalIter=sortedTreeMapCountryCapital.keySet().iterator();//put debug point at this line  
        while(countryCapitalIter.hasNext())  
        {  
            Country countryObj=countryCapitalIter.next();  
            String capital=countryCapitalMap.get(countryObj);  
            System.out.println(countryObj.getName()+"----"+capital);  
            }  
        }  

}

</country></country></country></country>

package org.arpit.java2blog;

import java.util.HashMap;

import java.util.Iterator;

import java.util.TreeMap;

public class TreeMapCompMain {

public static void main(String[] args)

{

Country india=new Country("India",1000);

Country japan=new Country("Japan",10000);

Country france=new Country("France",2000);

Country russia=new Country("Russia",20000);

HashMap<country string> countryCapitalMap=new HashMap<country>();

countryCapitalMap.put(india,"Delhi");

countryCapitalMap.put(japan,"Tokyo");

countryCapitalMap.put(france,"Paris");

countryCapitalMap.put(russia,"Moscow");

System.out.println("Sorting HashMap by passing it to TreeMap constructor");

TreeMap<country> sortedTreeMapCountryCapital=new TreeMap<country> (countryCapitalMap);

Iterator countryCapitalIter=sortedTreeMapCountryCapital.keySet().iterator();//put debug point at this line

while(countryCapitalIter.hasNext())

{

Country countryObj=countryCapitalIter.next();

String capital=countryCapitalMap.get(countryObj);

System.out.println(countryObj.getName()+"----"+capital);

}

</country></country></country></country>

When you run program, you will get below output:


Sorting HashMap by passing it to TreeMap constructor
France----Paris
India----Delhi
Japan----Tokyo
Russia----Moscow

Sorting HashMap by passing it to TreeMap constructor

France----Paris

India----Delhi

Japan----Tokyo

Russia----Moscow

Sorting by values example:

Here we will sort HashMap by its values. Here I am taking HashMap to make example simpler.
Example:


package org.arpit.java2blog;

import java.util.Collections;
import java.util.Comparator;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.ArrayList;
import java.util.List;
import java.util.Map.Entry;
import java.util.Set;

public class HashMapMain {

 public static void main(String args[]) {
  // HashMap with Country name as key and capital as value
  // HashMap stores elements in key value pairs
  HashMap<string string> countryCapitalMap = new HashMap<string string>();

  countryCapitalMap.put("Japan", "Tokyo");
  countryCapitalMap.put("France", "Paris");
  countryCapitalMap.put("Russia", "Moscow");
  countryCapitalMap.put("India", "Delhi");

  System.out.println("-----------------------------");
  // Iterating HashMap Using keySet() and for each loop
  System.out.println("Before Sorting");
  System.out.println("-----------------------------");
  for (String countryKey : countryCapitalMap.keySet()) {
   System.out.println("Country:" + countryKey + " and  Capital:" + countryCapitalMap.get(countryKey));

  }

  Set<entry string>> countryCapitalEntrySet=countryCapitalMap.entrySet();

  List<entry string>> entryList=new ArrayList<entry string>>(countryCapitalEntrySet);

  Collections.sort(entryList,new Comparator<entry>>() {

   @Override
   public int compare(Entry<string> o1, Entry<string> o2) {
    return o1.getValue().compareTo(o2.getValue());
   }
  });
  System.out.println("-----------------------------");

  // Using LinkedHashMop to keep entries in sorted order
  LinkedHashMap<string> sortedHashMap=new LinkedHashMap<string>();
  for (Entry<string> entry:entryList) {
   sortedHashMap.put(entry.getKey(), entry.getValue());
  }

  System.out.println("After Sorting");
  System.out.println("-----------------------------");
  // Iterating sortedHashMap Using keySet() and for each loop

  for (String countryKey : sortedHashMap.keySet()) {
   System.out.println("Country:" + countryKey + " and  Capital:" + sortedHashMap.get(countryKey));

  }
 }
}</string></string></string></string></string></entry></entry></entry></entry></string></string>

package org.arpit.java2blog;

import java.util.Collections;

import java.util.Comparator;

import java.util.HashMap;

import java.util.LinkedHashMap;

import java.util.ArrayList;

import java.util.List;

import java.util.Map.Entry;

import java.util.Set;

public class HashMapMain {

public static void main(String args[]) {

// HashMap with Country name as key and capital as value

// HashMap stores elements in key value pairs

HashMap<string string> countryCapitalMap = new HashMap<string string>();

countryCapitalMap.put("Japan", "Tokyo");

countryCapitalMap.put("France", "Paris");

countryCapitalMap.put("Russia", "Moscow");

countryCapitalMap.put("India", "Delhi");

System.out.println("-----------------------------");

// Iterating HashMap Using keySet() and for each loop

System.out.println("Before Sorting");

System.out.println("-----------------------------");

for (String countryKey : countryCapitalMap.keySet()) {

System.out.println("Country:" + countryKey + " and Capital:" + countryCapitalMap.get(countryKey));

}

Set<entry string>> countryCapitalEntrySet=countryCapitalMap.entrySet();

List<entry string>> entryList=new ArrayList<entry string>>(countryCapitalEntrySet);

Collections.sort(entryList,new Comparator<entry>>() {

@Override

public int compare(Entry<string> o1, Entry<string> o2) {

return o1.getValue().compareTo(o2.getValue());

}

});

System.out.println("-----------------------------");

// Using LinkedHashMop to keep entries in sorted order

LinkedHashMap<string> sortedHashMap=new LinkedHashMap<string>();

for (Entry<string> entry:entryList) {

sortedHashMap.put(entry.getKey(), entry.getValue());

}

System.out.println("After Sorting");

System.out.println("-----------------------------");

// Iterating sortedHashMap Using keySet() and for each loop

for (String countryKey : sortedHashMap.keySet()) {

System.out.println("Country:" + countryKey + " and Capital:" + sortedHashMap.get(countryKey));

}

}</string></string></string></string></string></entry></entry></entry></entry></string></string>

When you run above program, you will get below output


-----------------------------
Before Sorting
-----------------------------
Country:France and  Capital:Paris
Country:Russia and  Capital:Moscow
Country:Japan and  Capital:Tokyo
Country:India and  Capital:Delhi
-----------------------------
After Sorting
-----------------------------
Country:India and  Capital:Delhi
Country:Russia and  Capital:Moscow
Country:France and  Capital:Paris
Country:Japan and  Capital:Tokyo

-----------------------------

Before Sorting

-----------------------------

Country:France and Capital:Paris

Country:Russia and Capital:Moscow

Country:Japan and Capital:Tokyo

Country:India and Capital:Delhi

-----------------------------

After Sorting

-----------------------------

Country:India and Capital:Delhi

Country:Russia and Capital:Moscow

Country:France and Capital:Paris

Country:Japan and Capital:Tokyo

Explanation:

Extract key set from HashMap using keySet() method.
Create ArrayList from above set
Sort above ArrayList using Comparator
Create LinkedHashMap from Sorted list

Was this post helpful?

Let us know if this post was helpful. Feedbacks are monitored on daily basis. Please do provide feedback as that\'s the only way to improve.

How to sort HashMap in java by keys and values

Java HashMap tutorial:

Sorting by Keys:

Sorting by values:

Sorting by Keys example :

Sorting by values example:

Explanation:

Was this post helpful?

Author

Leave a Reply Cancel reply

Categories

Popular Posts

Let’s be Friends

Java HashMap tutorial:

Sorting by Keys:

Sorting by values:

Sorting by Keys example :

Sorting by values example:

Explanation:

Was this post helpful?

Related posts:

Share this

Author

Leave a Reply Cancel reply

Let’s be Friends