The java.util.Map interface is the root interface of the map hierarchy. Interestingly, it doesn’t extend the familiar java.util.Collection interface. It facilitates storage, retrieval, and manipulation of key-value pairs.

The popular implementations of Map are java.util.HashMap andjava.util.TreeMap. The HashMap facilitates easy insertion, deletion, and retrieval of elements. On the other hand, TreeMap is a neat alternative to traverse the keys of a map in a sorted order.

 // MapDemo.javaimport java.util.*;/** Demonstrates the use of popular java.util.Map implementations. */public class MapDemo {  /** The hash map to add data. */  private HashMap hashMap;  /** The tree map to sort data. */  private TreeMap treeMap;  /** Starts the demo. */  public void startDemo() {    // Initialize the hash map    hashMap = new HashMap();    hashMap.put(