What is the difference between hashmap, hashtable and hashset

Hashmap:

• Hash table implements Map interface
• Hash table permits null values and the null key
• HashMap class is equivalent to Hashtable, except that it is unsynchronized and permits nulls
• It does not guarantee that the order will remain constant over time
• constant-time performance for the operations (get, put and remove)
•  Time complexity - O(1) for get, put and remove

                (Learn About capacity , load factor and fail-fast)

• It is not synchronized
• How to make Hashmap Synchronize

                 Map m = Collections.synchronizedMap(new HashMap(...));

• Exapmle:

                   import java.util.*;

                   public class HashMapEx{

                   public static void main(String args[]) {

                  // Create a hash map

                     HashMap h = new HashMap();

                  // Put elements to the map

                     h.put(1,"x");

                     h.put(2,"y");

                     h.put(3,"z");

                    System.out.println(h.get("1"));

                     }

                   }

Hashtable: