1. Introduction

ConcurrentHashMap is a part of the Java Collections Framework designed for concurrent use by multiple threads. It provides thread-safety without synchronizing the entire map, thus ensuring high performance. In this guide, we will explore the CRUD (Create, Read, Update, Delete) operations on a ConcurrentHashMap.

2. Program Steps

1. Initialize a ConcurrentHashMap.

2. Populate the ConcurrentHashMap with key-value pairs (Create).

3. Retrieve a value by its key from the ConcurrentHashMap (Read).

4. Modify the value of an existing key (Update).

5. Remove a key-value pair from the ConcurrentHashMap (Delete).

6. Display the final state of the ConcurrentHashMap.

3. Code Program

import java.util.concurrent.ConcurrentHashMap;

public class ConcurrentHashMapCRUDExample {
    public static void main(String[] args) {
        // 1. Initialize a ConcurrentHashMap
        ConcurrentHashMap<String, Integer> scores = new ConcurrentHashMap<>();

        // 2. Populate the ConcurrentHashMap with key-value pairs (Create)
        scores.put("Alice", 90);
        scores.put("Bob", 85);
        scores.put("Charlie", 88);
        System.out.println("Initial ConcurrentHashMap: " + scores);

        // 3. Retrieve a value by its key from the ConcurrentHashMap (Read)
        int aliceScore = scores.get("Alice");
        System.out.println("Score of Alice: " + aliceScore);

        // 4. Modify the value of an existing key (Update)
        scores.put("Alice", 92);
        System.out.println("Updated score of Alice: " + scores.get("Alice"));

        // 5. Remove a key-value pair from the ConcurrentHashMap (Delete)
        scores.remove("Bob");
        System.out.println("After deleting Bob&apos;s score: " + scores);

        // 6. Display the final state of the ConcurrentHashMap
        System.out.println("Final ConcurrentHashMap: " + scores);
    }
}

Output:

Initial ConcurrentHashMap: {Alice=90, Bob=85, Charlie=88}
Score of Alice: 90
Updated score of Alice: 92
After deleting Bob's score: {Alice=92, Charlie=88}
Final ConcurrentHashMap: {Alice=92, Charlie=88}

4. Step By Step Explanation

1. We start by creating a ConcurrentHashMap instance using its default constructor.

2. The put method is used to insert key-value pairs into the ConcurrentHashMap.

3. We retrieve the value associated with a particular key using the get method.

4. To modify the value of an existing key, we use the put method with a key that already exists in the map.

5. We utilize the remove method to delete a specified key-value pair from the ConcurrentHashMap.

6. Throughout the program, we display the state of the ConcurrentHashMap at various stages to track the changes.

This guide provides a basic overview of the CRUD operations on a ConcurrentHashMap in Java, highlighting its concurrent properties that ensure thread-safety.