Linked HashMap in Java

Like a HashMap, a LinkedHashMap allows you to store key-value pairs and retrieve values based on their keys. However, unlike a HashMap, a LinkedHashMap maintains the order of the elements based on the order in which they were added to the map. This means that LinkedHashMap provides constant time complexity O(1) for add, remove, and search operations, but requires slightly more memory to maintain the order of the elements.

Here are some key features of a LinkedHashMap in Java:

Tweet

1. Unique keys: Each key in a LinkedHashMap must be unique. If you try to add a key that already exists in the LinkedHashMap, the value associated with the key will be updated to the new value.
2. Null keys and values: A LinkedHashMap implementation allows null keys and null values. This means that you can add key-value pairs where the key or value is null.
3. Maintains order: The order of the key-value pairs in a LinkedHashMap is maintained based on the order in which they were added to the map.

import java.util.LinkedHashMap;
import java.util.Map;

public class LinkedHashMapExample {
    public static void main(String[] args) {
        // create a new LinkedHashMap
        Map<String, Integer> scores = new LinkedHashMap<>();

        // add some key-value pairs to the map
        scores.put("Alice", 100);
        scores.put("Bob", 90);
        scores.put("Charlie", 80);

        // get the value associated with a key
        int aliceScore = scores.get("Alice");
        System.out.println("Alice's score is " + aliceScore);

        // iterate through the key-value pairs in the map
        for (Map.Entry<String, Integer> entry : scores.entrySet()) {
            String name = entry.getKey();
            int score = entry.getValue();
            System.out.println(name + " scored " + score + " points.");
        }
    }
}

In this example, we create a new LinkedHashMap and add some key-value pairs to it. We then retrieve the value associated with the “Alice” key using the get() method, and iterate through all the key-value pairs in the map using a for-each loop over the entrySet(). Since LinkedHash