How to Iterate a HashMap of ArrayLists of String in Java

This Java program shows how to iterate a HashMap that contains arraylists of String.

In the Java program to iterate a HashMap containing ArrayLists there is a method getMap() where 3 lists are created and stored in the HashMap.

First you need to iterate the HashMap, though there are several ways to iterate over a HashMap, but here I have used the for-each loop for iterating the created HashMap. Each Map.Entry object is a key-value pair where value is the ArrayList stored with the given key. That's the list retrieved using listEntry.getValue() method.

In the second for-each loop List that is retrieved using listEntry.getValue() is iterated and the elements that are in the list are displayed.

Java Program to Iterate HashMap of ArrayLists

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class MapLoop {

  public static void main(String[] args) {
    MapLoop mapLoop = new MapLoop();
    Map<String, List<String>> cityMap = mapLoop.getMap();
    int i = 0;
    // iterating over a map
    for(Map.Entry<String, List<String>> listEntry : cityMap.entrySet()){
      System.out.println("Iterating list number - " + ++i);
      // iterating over a list
      for(String cityName : listEntry.getValue()){
        System.out.println("City - " + cityName);
      }
    }
  }
    
  /**
   * A method to create a list and store it in a Map
   * @return
  */
  private Map<String, List<String>> getMap(){
    Map<String, List<String>> cityMap = new HashMap<String, List<String>>();
    // First List
    List<String> temp = new ArrayList<String>();  
    temp.add("Delhi");
    temp.add("Mumbai");
    // Putting first list in the map
    cityMap.put("1", temp);
    // Second List
    temp = new ArrayList<String>();  
    temp.add("Hyderabad");
    temp.add("Bangalore");
    // Putting second list in the map
    cityMap.put("2", temp);
    // Third List
    temp = new ArrayList<String>();
    temp.add("Kolkata");
    temp.add("Chennai");
    // Putting third list in the map
    cityMap.put("3", temp);
    return cityMap;
  }
}

Output

Iterating list number - 1
City - Delhi
City - Mumbai
Iterating list number - 2
City - Hyderabad
City - Bangalore
Iterating list number - 3
City - Kolkata
City - Chennai

That's all for this topic How to iterate a Hash map of arraylists of String in Java. If you have any doubt or any suggestions to make please drop a comment. Thanks!

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