Unordered Data using HashMap in Java

Understanding through Code

import java.util.HashMap;  import java.util.Map;    public class HashMapDemo {  	public static void main( String[] args ){  		Map<String, String> map = new HashMap<>();    		map.put("India", "First");  		map.put("US", "Second");  		map.put("Canada", "Third");  		System.out.println(map);    		map.put("Russia", "Fourth");  		System.out.println(map);    		String mapString = map.get("US");  		System.out.println("The US stands at: " +mapString);    		System.out.println(mapString);  		map.remove("Russia");  		  	}  }

Output

• {Canada=Third, US=Second, India=First}
• {Canada=Third, US=Second, India=First, Russia=Fourth}
• The US stands at: Second
• Second

Notes

• HashMap is unordered data collection.
• HashMap is implementation of Map. Just like ArrayList is an implementation of List.
• Maps are in Key, Value pairs.
• You can look up an item in HashMap with the help of Key.