Java HashMap example

HashMap is an object that stores both “key/value” as a pairs. In this article, we show you how to create a HashMap instance and iterates the HashMap data.

["mkyong","1000.00"] = ["key","value"]

In above, “mkyong” is the key , “1000.00” is the value. By given a key “mkyong”, you can get the value “1000.00”.

Example

See full example of using HashMap.

package com.mkyong.core;
 
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
 
public class Number {
	public static void main(String[] args) {
		try {
 
			Map mMap = new HashMap();
			mMap.put("PostgreSQL", "Free Open Source Enterprise Database");
			mMap.put("DB2", "Enterprise Database , It's expensive");
			mMap.put("Oracle", "Enterprise Database , It's expensive");
			mMap.put("MySQL", "Free Open SourceDatabase");
 
			Iterator iter = mMap.entrySet().iterator();
 
			while (iter.hasNext()) {
				Map.Entry mEntry = (Map.Entry) iter.next();
				System.out.println(mEntry.getKey() + " : " + mEntry.getValue());
			}
 
			mMap.put("Oracle", "Enterprise Database , It's free now ! (hope)");
 
			System.out.println("One day Oracle.. : " + mMap.get("Oracle"));
 
		} catch (Exception e) {
			System.out.println(e.toString());
		}
	}
}

Output

PostgreSQL : Free Open Source Enterprise Database
MySQL : Free Open SourceDatabase
Oracle : Enterprise Database , It's expensive
DB2 : Enterprise Database , It's expensive
One day Oracle.. : Enterprise Database , It's free now ! (hope)
Tags :

About the Author

mkyong
Founder of Mkyong.com and HostingCompass.com, love Java and open source stuff. Follow him on Twitter, or befriend him on Facebook or Google Plus. If you like my tutorials, consider make a donation to these charities.

Comments

  • Nicky Larson

    Thank you man !

  • fasfas

    not bad../

  • Bikash

    Simple and nice tutorial, but I have a problem where I need to keep track of number of occurrence of words every time I found that words in text. So I would like to know will HashMap will be good solution for me. Thanks

  • scqed

    Great example, but can you comment on the compiler warning about hashmap being a generic type that it should be parameterized?

    • htmlman1

      It’s asking for something like this:

      HashMap foo = new HashMap ();

      Here instead of a “generic type” you’re specifying a specific type (i.e. the Integer.)
      If you’re making a hashmap to store strings you could do something like this:

      HashMap foo = new HashMap();

      This would prevent the “generic type” warning.

  • sivaraj

    Sir Pls help me, i stored the keys and Values.. I can get the value from the hash map, bt not in ordered.. i got it shuffled.. So how to get the HashMap values by the order, what i stored..

  • Ram Ramachandran

    Good Work, Simple and Clear

  • http://topinfonews.com TIN Sam

    This website is cool. Java is cool too. I just finish TPL program, and i used HashMap to store certain things. it makes my work simple and faster. http://vibeink.com

  • http://www.maritha-myworldmydream.blogspot.com Maritha

    Hi There ! I’m from Indonesia and I’d like to ask how we’d show up the Key if we input the value. imagine I’m making dictionary coding using Map in Java. there my email, please so small reply to my email, I’d appreciate it if U share. Thank you, Mkyong !

    • http://topinfonews.com TIN Sam

      Hello @Maritha, if am not mistaken u are asking how to display ur hashmap values? if yes Map.values() will return collection of value in the map. u can use get to return each value by key. http://vibeink.com

  • SHAFF

    Very Good Example,
    I have a dout..i am adding key and value to hash map value as arraylist.
    (data getting from data base)
    i want to display the key values in jsp page.
    key — Time interval(24 hours)
    Value –(login,uniqlogins)
    if record is not there for particular interval then how i assign a key and value(default 0,0).
    Ex: Time Interval : 00-23
    for 3,4,5,6,7 there is no records for this interval
    then i need to add 0,0 to values for that particular key.
    please help me thanksin advance…

  • http://www.lolligroove.com Daniel o

    Hello MKYONG, I am thinking of a network monitoring system as as my final year project
    can u give any help as to how to start and what is required (Java)

    • http://www.maritha-myworldmydream.blogspot.com Maritha

      a network monitoring system ? awesome.

  • JavaLover

    Really nice & simple program to illustrate Hash. Add tweet button. I’ll tweet this!!!

  • http://indiabusinessads.com saphna

    clear and concise example of hashmap :)

  • Rajiv

    Good Example for beginners, though I read couple of article on hashmap I found your example most simple and How HashMap works in Java theory most useful. Thanks

  • Anonymous

    Thanks, good and simple example

  • @mey

    gud example….!

  • Rakesh

    good explanation of basic stuff in HashMap. I also found this link worth checking How HashMap works in Java

  • http://javarevisited.blogspot.com/ Javin Paul

    HashMap is very useful class in java but most people don’t understand difference between HashMap and Hashtable and when to use which , its important to learn correct usage of collection classes. to read about Hashtable vs HashMap see .

    Cheers
    Javin

  • soumya

    hi,

    This is very very good website for java and open source tutorials.

    thanks

  • tapan(i want use map in java and use map in create chat module)

    please give me a chat mpdule while using a map please….?

    • http://www.mkyong.com mkyong

      please send your project to my email , will consult and give some comments.