Can you explain what a LinkedHashMap in Java is and what features it has?

LinkedHashMap in Java is an implementation of the Map interface that maintains the order of insertion of elements.

Features of LinkedHashMap:

• Elements are stored as key-value pairs, like in HashMap.
• Unlike HashMap, LinkedHashMap maintains a linked list of the entries, which allows iteration in the order of insertion.
• It supports access order, which is useful for implementing caches with LRU (least recently used) policy.
• Access, insertion, and removal times are approximately O(1), similar to HashMap.

Example usage:

import java.util.LinkedHashMap;

public class Example {
    public static void main(String[] args) {
        LinkedHashMap<Integer, String> map = new LinkedHashMap<>();
        map.put(1, "one");
        map.put(2, "two");
        map.put(3, "three");

        // Iteration in insertion order
        for (Integer key : map.keySet()) {
            System.out.println(key + " -> " + map.get(key));
        }
    }
}

The output will be in the order 1, 2, 3, which is not guaranteed in a regular HashMap.