1. Introduction

The HashMap class in Java, part of the java.util package, stores key-value pairs. To determine if a HashMap instance is empty, we can use the isEmpty() method. This method returns a boolean value: true if the map contains no key-value mappings, and false otherwise. In this post, we will create a simple program demonstrating the use of the isEmpty() method.

2. Program Steps

1. Create a HashMap and check if it is empty using the isEmpty() method.

2. Populate the HashMap with some key-value pairs.

3. Again, check if the updated HashMap is empty using the isEmpty() method.

3. Code Program

import java.util.HashMap;
import java.util.Map;

public class HashMapIsEmpty {

    public static void main(String[] args) {

        // Step 1: Create a HashMap and check if it is empty
        Map<String, Integer> map = new HashMap<>();
        System.out.println("Is the HashMap empty? " + map.isEmpty());

        // Step 2: Populate the HashMap with some key-value pairs
        map.put("One", 1);
        map.put("Two", 2);
        map.put("Three", 3);

        // Step 3: Again, check if the updated HashMap is empty
        System.out.println("Is the updated HashMap empty? " + map.isEmpty());
    }
}

Output:

Is the HashMap empty? true
Is the updated HashMap empty? false

4. Step By Step Explanation

Step 1: A HashMap named map is created. Initially, it has no key-value pairs. The isEmpty() method is called to check whether map is empty, which returns true.

Step 2: We add three key-value pairs to the HashMap. Now, map is no longer empty.

Step 3: We again check if map is empty using the isEmpty() method. This time, it returns false as there are key-value pairs present in the HashMap.