How many ways can convert HashMap to List in Java and using Java8

Hi,

Today we will talk about how we can convert Hashmap into ArrayList.

1. we have converted keys of HashMap into List.

2. we have converted all values of Map into List.

3. we have converted all entries(key & values) of HashMap into List.

In below i have explained program stepwise:-

 package com.neesri.sorting;

import java.util.ArrayList;
import java.util.Collection;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map.Entry;
import java.util.Set;
import java.util.stream.Collectors;

public class ConvertMapToList {
 // we can convert Hashmap into Arraylist through three ways
 public static void main(String[] args) {

  HashMap<String, Integer> hashmapObj = new HashMap<>();
  hashmapObj.put("Zimbabwe", 600);
  hashmapObj.put("India", 700);
  hashmapObj.put("SriLanka", 400);
  hashmapObj.put("Nepal", 800);

  // 1-----convert Hashmap Key into List
  // using keyset method retun set view
  Set<String> setViewOfMapKeys = hashmapObj.keySet();
  // convert set into list
  List<String> listObj = new ArrayList<>(setViewOfMapKeys);

  System.out.println("Hashmap Keys into list-------------------------------->");
  for (String printList : listObj) {
   System.out.println(printList);
  }
  // ---------------------using java8 stream -----------------------------

  System.out.println("Hashmap Keys into list using Java8 Stream ------------->");
  List<String> listJava8_forKey = hashmapObj.keySet().stream().collect(Collectors.toList());
  listJava8_forKey.forEach(System.out::println);

  // 2. Convert Hashmap Values into List

  Collection<Integer> values = hashmapObj.values();
  List<Integer> list = new ArrayList<>(values);
  System.out.println("Hashmap values into List-------------------------------->");
  for (Integer hashmapValuesIntoList : list) {
   System.out.println(hashmapValuesIntoList);
  }

  // ---------------------using java8 stream -----------------------------
  System.out.println("Hashmap values into List using Java8 Stream---------------->");
  List<Integer> listjava8_forValues = hashmapObj.values().stream().collect(Collectors.toList());
  listjava8_forValues.forEach(System.out::println);

  // 3. Convert hashmap all entries into List

  Set<Entry<String, Integer>> entriesObjSet = hashmapObj.entrySet();
  List<Entry<String, Integer>> listEntries = new ArrayList<>(entriesObjSet);

  // System.out.println("Hashmap all entries into List======>");
  /*
   * for(Object obj:listEntries) {
   * 
   * System.out.println(obj); }
   */
  // OR

  /*
   * for(Entry<String, Integer> obj:listEntries) {
   * 
   * System.out.println(obj); }
   */

  // OR
  System.out.println("Printing thorough iterator======================>");
  Iterator<Entry<String, Integer>> iterator = listEntries.iterator();

  while (iterator.hasNext()) {
   Entry<String, Integer> entry = iterator.next();

   System.out.println(entry);
  }

  //
  System.out.println("Hashmap ALL entries thorugh JAVA 8 Stream===============>");
  List<Entry<String, Integer>> listjava8_allentries = hashmapObj.entrySet().stream().collect(Collectors.toList());
  listjava8_allentries.forEach(System.out::println);
 }

}

output → Hashmap Keys into list — — — — — — — — — — — — — — — →

SriLanka

Zimbabwe

Nepal

India

Hashmap Keys into list using Java8 Stream — — — — — — ->

SriLanka

Zimbabwe

Nepal

India

Hashmap values into List — — — — — — — — — — — — — — — →

400

600

800

700

Hashmap values into List using Java8 Stream — — — — — — — →

400

600

800

700

Printing thorough iterator======================>

SriLanka=400

Zimbabwe=600

Nepal=800

India=700

Hashmap ALL entries thorugh JAVA 8 Stream===============>

SriLanka=400

Zimbabwe=600

Nepal=800

India=700