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Java HashMap Example

Submitted by Andr on Tue, 10/26/2010 - 19:53

Java Examples

/*
Java HashMap example.
This Java HashMap example describes the basic operations performed on the HashMap.
*/
 
import java.util.HashMap;
import java.util.Iterator;
 
public class HashMapExample{
    
    public static void main(String args[]){
       
        // constructs a new empty HashMap with default initial capacity        
        HashMap hashMap = new HashMap();
       
        /*
       
        To specify initial capacity, use following constructor        
        HashMap HashMap = new HashMap(100);
       
        To create HashMap from map use following constructor        
        HashMap HashMap = new HashMap(Map myMap);
       
        */
       
        hashMap.put("One", new Integer(1)); // adding value into HashMap
       
        hashMap.put("Two", new Integer(2));
       
        hashMap.put("Three", new Integer(3));
       
        /*
        IMPORTANT : We CAN NOT add primitives to the HashMap. We have to wrap it into
        one of the wrapper classes before adding.
        */
       
        /*
       
        To copy all key - value pairs from any Map to HashMap use putAll method.
        Signature of putAll method is,        
        void putAll(Map m)
       
        */
       
        //get number of keys present in the HashMap        
        System.out.println("HashMap contains " + hashMap.size() + " key value pairs.");
       
        /*
       
        To check whether HashMap is empty or not, use isEmpty() method.        
        isEmpty() returns true is HashMap is empty, otherwise false.
       
        /*
       
        Finding particular value from the HashMap:
       
        HashMap's containsValue method returns boolean depending upon
        the presence of the value in given HashMap
       
        Signature of the containsValue method is,        
        boolean containsValue(Object value)
       
        */
       
        if(hashMap.containsValue(new Integer(1))){
            System.out.println("HashMap contains 1 as value");
        }else{
            System.out.println("HashMap does not contain 1 as value");
        }
       
        /*
       
        Finding particular Key from the HashMap:        
        HashMap's containsKey method returns boolean depending upon the
        Presence of the key in given HashMap
       
        Signature of the method is,        
        boolean containsKey(Object key)
       
        */
       
        if( hashMap.containsKey("One") ){
            System.out.println("HashMap contains One as key");
        }else{
            System.out.println("HashMap does not contain One as value");
        }
       
        /*
        Use get method of HashMap to get value mapped to particular key.        
        Signature of the get method is,        
        Object get(Object key)        
        */
       
        Integer one = (Integer) hashMap.get("One");        
        System.out.println("Value mapped with key \"One\" is " + one);
       
        /*
        IMPORTANT:  get method returns Object, so we need to downcast it.
        */
       
        /*
        To get all keys stored in HashMap use keySet method        
        Signature of the keysSet method is,        
        Set keySet()
        */
       
        System.out.println("Retrieving all keys from the HashMap");        
        Iterator iterator = hashMap.keySet().iterator();
       
        while(iterator. hasNext()){        
            System.out.println(iterator.next());
        }
       
        /*
        To get all values stored in HashMap use entrySet() method.
        Signature of the entrySet() method is,        
        Set entrySet()
        */
       
        System.out.println("Retrieving all values from the HashMap");
        iterator = hashMap.entrySet().iterator();
       
        while(iterator. hasNext()){        
            System.out.println(iterator.next());
        }
       
        /*
        To remove particular key - value pair from the HashMap use remove method.        
        Signature of remove method is,        
        Object remove(Object key)        
        This method returns value that was mapped to the given key,
        otherwise null if mapping not found.
       
        */
       
        System.out.println( hashMap.remove("One") + " is removed from the HashMap.");
       
    }
 
}
 
/*
OUTPUT of the above given Java HashMap Example would be :
HashMap contains 3 key value pair.
HashMap contains 1 as value
HashMap contains One as key
Value mapped with key "One" is 1
Retrieving all keys from the HashMap
Three
Two
One
Retrieving all values from the HashMap
Three=3
Two=2
One=1
1 is removed from the HashMap.
*/

Andr's blog

10x for U !

Submitted by Anonymous on Sat, 12/04/2010 - 21:51.

10x for U !

!!!!!!!!!!!!!!!!!!!!!!!!!

Submitted by Anonymous on Mon, 03/14/2011 - 16:29.

!!!!!!!!!!!!!!!!!!!!!!!!!

nicw code buddy....really

Submitted by Anonymous on Wed, 04/27/2011 - 15:02.

nicw code buddy....really useful

Indeed simple and effective

Submitted by Anonymous on Fri, 12/23/2011 - 10:05.

Indeed simple and effective code example to learn hashmap, but on theory part I really like How HashMap works in Java which is based on inner working of hashmap.

Thanks for this class.Its

Submitted by Anonymous on Wed, 12/22/2010 - 22:58.

Thanks for this class.Its very helpful.I would recommend this to anyone who is trying to get hold of HashMap API

is this true??

Submitted by Anonymous on Mon, 01/10/2011 - 12:29.

is this true??

ya....its very good code to

Submitted by Anonymous on Wed, 04/27/2011 - 01:51.

ya....its very good code to learn on hashmap

completely agree nice and

Submitted by Anonymous on Sun, 07/03/2011 - 10:05.

completely agree nice and easy code that's what I was looking for. for theory pat though I found How HashMap works in Java quite useful.

Thnx it really helpfull

Submitted by Anonymous on Tue, 02/08/2011 - 16:08.

Thnx it really helpfull

i love the way presentation

Submitted by Anonymous on Thu, 02/17/2011 - 21:09.

i love the way presentation was.:)

thank u:)

Submitted by Anonymous on Fri, 03/04/2011 - 12:28.

thank u:)

Thanks buddy!

Submitted by Anonymous on Sun, 03/06/2011 - 01:38.

Thanks buddy!

well commented source code i

Submitted by Anonymous on Tue, 03/08/2011 - 21:40.

well commented source code i love it

well commented source code i

Submitted by Anonymous on Tue, 03/08/2011 - 21:40.

well commented source code i love it

Thanks

Submitted by Anonymous on Wed, 03/23/2011 - 15:56.

Thanks

Thanks its very handy.. :)

Submitted by Anonymous on Wed, 03/23/2011 - 17:02.

Thanks its very handy.. :)

hey hot to creat a array of

Submitted by Anonymous on Sat, 03/26/2011 - 19:33.

hey hot to creat a array of hashmap..for example i want fetch a data from database and store it in a result set object..this may contain any number of rows...i want copy those resultset data to the hashmap...can we do that through hashmap..thanks in advance

Thanks for the example -

Submitted by Anonymous on Thu, 03/31/2011 - 16:28.

Thanks for the example - Ketan

Simple and easy way to

Submitted by Anonymous on Thu, 05/26/2011 - 10:57.

Simple and easy way to understand hashmap. good one

Thank you. Good work.

Submitted by Anonymous on Mon, 04/04/2011 - 17:12.

Thank you. Good work.

Really great tutorial...Love

Submitted by Anonymous on Tue, 04/12/2011 - 17:02.

Really great tutorial...Love it...

Thanks for the good example!

Submitted by Anonymous on Tue, 04/12/2011 - 19:38.

Thanks for the good example!

Well constructed .. looks

Submitted by Anonymous on Wed, 04/13/2011 - 19:38.

Well constructed .. looks neat... superlike :)

Great tutorial Understood it

Submitted by Anonymous on Wed, 04/13/2011 - 23:59.

Great tutorial Understood it in just 15 minutes. SuperLike :)))))))))))))

:)

Submitted by Anonymous on Thu, 04/21/2011 - 11:35.

nice one...:)

Submitted by Anonymous on Tue, 04/26/2011 - 11:45.

nice one...:)

excellent tutorial for

Submitted by Anonymous on Tue, 05/03/2011 - 11:55.

excellent tutorial for beginners! Thanks a lot !!

Good Presentation

Submitted by Anonymous on Wed, 05/04/2011 - 15:44.

Good Presentation

Superb code.... please keep

Submitted by Anonymous on Sat, 05/07/2011 - 07:21.

Superb code.... please keep coding this way...

Should have used Generics as

Submitted by Anonymous on Tue, 05/10/2011 - 17:54.

Should have used Generics as well

Excellent Code to learn

Submitted by Anonymous on Mon, 05/16/2011 - 23:20.

Excellent Code to learn HashMap

thanks u , sweet and simple

Submitted by Anonymous on Tue, 05/17/2011 - 23:42.

thanks u , sweet and simple

tnks man. really really good

Submitted by Anonymous on Tue, 05/31/2011 - 09:21.

tnks man. really really good explanation. cheers from brazil.

Excellent Code to learn

Submitted by Anonymous on Wed, 06/01/2011 - 14:37.

Excellent Code to learn HashMap

thankx it is really helpful

Submitted by Anonymous on Thu, 06/02/2011 - 12:23.

thankx it is really helpful

chimpenav ..........good code

Submitted by Anonymous on Fri, 06/03/2011 - 15:22.

chimpenav ..........good code

ya gr8 code to learn abt

Submitted by Anonymous on Tue, 08/02/2011 - 18:20.

ya gr8 code to learn abt hashmap :) n1..

Thankyou

Submitted by Anonymous on Wed, 08/03/2011 - 11:57.

Thankyou

Well written, Thanks for that

Submitted by Anonymous on Mon, 08/29/2011 - 14:18.

Well written, Thanks for that very clean and understandable code

thank you , it is very

Submitted by Anonymous on Mon, 09/05/2011 - 09:26.

thank you , it is very helpfull

good raess

Submitted by Anonymous on Mon, 09/05/2011 - 12:11.

good raess

thank yu=ou

Submitted by Anonymous on Mon, 10/10/2011 - 15:44.

thank yu=ou

Nice post

Submitted by Anonymous on Wed, 10/19/2011 - 20:18.

Nice post

super cool example

Submitted by Anonymous on Thu, 10/20/2011 - 21:20.

super cool example

Goods.Thanks verymuch

Submitted by Anonymous on Tue, 10/25/2011 - 13:12.

Goods.Thanks verymuch

thank you very useful

Submitted by Anonymous on Sat, 10/29/2011 - 17:01.

thank you very useful tutorial

Nice tutorial, Clear consice

Submitted by Anonymous on Sun, 10/30/2011 - 13:20.

Nice tutorial, Clear consice code which explains the concepts of HashMap in a clean way. I have also added a small tutorial on how HashMap are implemented in the Java Memory Model, internally. You can check it out here

really tacky one should

Submitted by Anonymous on Mon, 10/31/2011 - 18:51.

really tacky one should better showed how to retrieve the elements from hashmap

How does one return a hashmap

Submitted by Anonymous on Thu, 11/03/2011 - 11:25.

How does one return a hashmap from a method ? I am trying this ?? Map get_sales () { HashMap map = new HashMap(); map.put("JAN", "15"); map.put("feb", "27"); map.put("march", "12"); return map; } Map x = get_sales (); // this does not seem to work ? Any ideas on how to implement this will be appreciated.