1. Introduction

In Java, HashMap is a part of the java.util package, and it implements the Map interface, storing elements in key/value pairs. However, sometimes you might need to convert a HashMap into an ArrayList. In this tutorial, we will discuss a straightforward approach to convert a HashMap into an ArrayList.

2. Program Steps

1. Create and initialize a HashMap.

2. Convert the keys of the HashMap into an ArrayList.

3. Convert the values of the HashMap into another ArrayList.

4. Print the two ArrayLists.

3. Code Program

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

public class HashMapToArrayList {

    public static void main(String[] args) {

        // Step 1: Create and initialize a HashMap
        Map<String, Integer> map = new HashMap<>();
        map.put("Apple", 10);
        map.put("Banana", 20);
        map.put("Cherry", 30);

        // Step 2: Convert the keys of the HashMap into an ArrayList
        List<String> keyList = new ArrayList<>(map.keySet());

        // Step 3: Convert the values of the HashMap into another ArrayList
        List<Integer> valueList = new ArrayList<>(map.values());

        // Step 4: Print the two ArrayLists
        System.out.println("Key List: " + keyList);
        System.out.println("Value List: " + valueList);
    }
}

Output:

Key List: [Apple, Banana, Cherry]
Value List: [10, 20, 30]

4. Step By Step Explanation

Step 1: A HashMap named map is created and initialized with three entries, each consisting of a String key and an Integer value.

Step 2: The keySet() method is used to get the keys from the HashMap, and a new ArrayList named keyList is created from this set.

Step 3: The values() method is used to get the values from the HashMap, and another ArrayList named valueList is created from this collection.

Step 4: Finally, both the keyList and the valueList are printed to the console, showcasing the conversion of the HashMap keys and values into ArrayLists.