1. Introduction

The HashMap class in Java is part of the java.util package and is used to store key-value pairs. The keySet() method of the HashMap class is utilized to retrieve all keys present in the map. It returns a Set view of the keys contained in the map. In this blog post, we will create a program to demonstrate the use of the keySet() method in a HashMap.

2. Program Steps

1. Create a HashMap and populate it with some key-value pairs.

2. Use the keySet() method to retrieve the keys from the HashMap.

3. Iterate through the retrieved keys and print them.

3. Code Program

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

public class HashMapKeySet {

    public static void main(String[] args) {

        // Step 1: Create a HashMap and populate it with some key-value pairs
        Map<String, Integer> map = new HashMap<>();
        map.put("One", 1);
        map.put("Two", 2);
        map.put("Three", 3);

        // Step 2: Use the keySet() method to retrieve the keys from the HashMap
        Set<String> keys = map.keySet();

        // Step 3: Iterate through the retrieved keys and print them
        System.out.println("Keys in the HashMap:");
        for(String key : keys) {
            System.out.println(key);
        }
    }
}

Output:

Keys in the HashMap:
One
Two
Three

4. Step By Step Explanation

Step 1: A HashMap named map is created and populated with three key-value pairs.

Step 2: The keySet() method is called on the map to retrieve the keys. This method returns a Set containing the keys, which is stored in the variable keys.

Step 3: An enhanced for loop is used to iterate through the Set of keys, and each key is printed to the console. The order of the keys in the output may vary, as HashMap does not guarantee any specific order of the keys.