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How to convert a HashMap to an ArrayList

Educative Answers Team

HashMap is a collection class, based on Maps, that stores key and value pairs; they are denoted as HashMap<Key, Value> or HashMap<K, V>.

ArrayList provides the dynamic arrays in Java. These arrays use an ​iterator to access the objects stored in the ArrayList.

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Conversion of HashMap to ArrayList

A HashMap contains key-value pairs, there are three ways to convert a HashMap to an ArrayList:

  1. Converting the HashMap keys into an ArrayList.

  2. Converting the HashMap values into an ArrayList.

  3. Converting the HashMap key-value pairs into an ArrayList.

The implementation of these three methods is shown below:

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
 
class HashMapToArrayListConversion {
 
 public static void main(String args[])
 {
  // HashMap with Country as key and capital as value
  
  HashMap<String,String> countryCapitalMap=
  new HashMap<String,String>();

  countryCapitalMap.put("USA","Washington");
  countryCapitalMap.put("Bangladesh","Dhaka");
  countryCapitalMap.put("France","Paris");
  countryCapitalMap.put("England","London");
  countryCapitalMap.put("Russia","Moscow");
 
 
  System.out.println("-----------------------------");
 
  // Creating  ArrayList from Keys
  
  ArrayList<String> keysArrayList=
  new ArrayList<String>(countryCapitalMap.keySet());

  System.out.println("Countries (Keys) are: ");
  for (String country: keysArrayList) {
    System.out.println(country);
}
 
  System.out.println("-----------------------------");
 
  //Creating  ArrayList from Values
  ArrayList<String> valuesArrayList=
  new ArrayList<String>(countryCapitalMap.values());
  System.out.println("Capital (Values) are: ");
  for (String capital:valuesArrayList) {
    System.out.println(capital);
}
  System.out.println("-----------------------------");
 
  //Creating  ArrayList from Entry set
  ArrayList <Entry <String,String>> entryArrayList=
  new ArrayList<Entry<String,String>>(countryCapitalMap.entrySet());
  for (Entry <String, String> entry:entryArrayList) {
    System.out.println("Country: "+ entry.getKey() 
    + " and  Capital: "+entry.getValue());
 
  }
 
 System.out.println("-----------------------------");
 
 }
}

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convert
hashmap
arraylist
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