Creating a Hash Map in java

This example shows how to create hash map and perform some operations on it.

public static Map createMap(){
  // Create a hash table 
  Map map = new HashMap();   // hash table
  //Map map = new TreeMap(); // you can do sorted 
  //map as well


  // Add key/value pairs to the map 
  map.put("a", 1);
  map.put("b", new Integer(2));
  map.put("c", new Integer(3));


  // Get number of entries in map 
  int size = map.size(); // 2

  // Adding an entry whose key exists in the map causes 

  // the new value to replace the old value 
  Object oldValue = map.put("a", new Integer(9)); // 1


// Remove an entry from the map and return the value of the removed entry 
  oldValue = map.remove("c"); // 3

  boolean isempty = map.isEmpty();

  return map;

 }

As putting a duplicate key value, pair changes value, use containsKey() and containsValue(), a programmer can check the existence of a key or value with the HashMap.