1. Introduction

LinkedHashMap is a subclass of HashMap that maintains a doubly-linked list running through all its entries. This ensures the order of the elements based on their insertion or access. In essence, this class allows insertion-order iteration over the map, meaning when iterating through the collection, elements will be returned in the order they were inserted. In this guide, we’ll explore the CRUD (Create, Read, Update, Delete) operations on a LinkedHashMap.

2. Program Steps

1. Initialize a LinkedHashMap.

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

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

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

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

6. Display the final state of the LinkedHashMap.

3. Code Program

import java.util.LinkedHashMap;

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

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

        // 3. Retrieve a value by its key from the LinkedHashMap (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 LinkedHashMap (Delete)
        scores.remove("Bob");
        System.out.println("After deleting Bob&apos;s score: " + scores);

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

Output:

Initial LinkedHashMap: {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 LinkedHashMap: {Alice=92, Charlie=88}

4. Step By Step Explanation

1. We begin by initializing an empty LinkedHashMap with String keys and Integer values.

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

3. Using the get method, we can retrieve the value associated with a particular key.

4. By using the put method with an existing key, we update the associated value.

5. The remove method is used to delete a specific key-value pair from the LinkedHashMap.

6. Throughout the program, we display the status of the LinkedHashMap to observe the changes.

From this tutorial, we learn the fundamental CRUD operations with respect to a LinkedHashMap in Java, emphasizing its insertion-order iteration capability.