Program: Basic HashMap Operations.

Below example shows basic HashMap functionalities like creating object, adding entries, getting values by passing key, checking is hashmap is empty or not, deleting an element and size of the HashMap.

package com.java2novice.hashmap;

import java.util.HashMap;

public class MyBasicHashMap {

	public static void main(String a[]){
		HashMap<String, String> hm = new HashMap<String, String>();
		//add key-value pair to hashmap
		hm.put("first", "FIRST INSERTED");
		hm.put("second", "SECOND INSERTED");
		hm.put("third","THIRD INSERTED");
		System.out.println(hm);
		//getting value for the given key from hashmap
		System.out.println("Value of second: "+hm.get("second"));
		System.out.println("Is HashMap empty? "+hm.isEmpty());
		hm.remove("third");
		System.out.println(hm);
		System.out.println("Size of the HashMap: "+hm.size());
	}
}

{second=SECOND INSERTED, third=THIRD INSERTED, first=FIRST INSERTED}
Value of second: SECOND INSERTED
Is HashMap empty? false
{second=SECOND INSERTED, first=FIRST INSERTED}
Size of the HashMap: 2