Create your own blog, earn points and get popular!

Java Hashtable Example

Submitted by Andr on Tue, 10/26/2010 - 19:46

Java Examples

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

Andr's blog

Great explanation

Submitted by Anonymous on Sun, 12/05/2010 - 22:27.

Great explanation

thanks

Submitted by Anonymous on Sun, 12/19/2010 - 03:14.

thanks

Thanks . Great Explanation

Submitted by Anonymous on Mon, 01/03/2011 - 13:54.

Thanks . Great Explanation

Thanks. quite strictly way to

Submitted by Anonymous on Wed, 01/12/2011 - 10:37.

Thanks. quite strictly way to explain the idea

The explanation is too good

Submitted by Anonymous on Mon, 01/24/2011 - 08:13.

The explanation is too good

An example that I was looking

Submitted by Anonymous on Tue, 01/25/2011 - 04:56.

An example that I was looking for. Thank you.

interesting

Submitted by Anonymous on Thu, 01/27/2011 - 06:25.

interesting

thank you

Submitted by Anonymous on Thu, 01/27/2011 - 06:27.

thank you

thanks dear

Submitted by Anonymous on Fri, 02/11/2011 - 15:10.

thanks dear

Thanks dude

Submitted by Anonymous on Wed, 02/16/2011 - 09:07.

Thanks dude

thank you for the nice

Submitted by Anonymous on Wed, 02/16/2011 - 23:18.

thank you for the nice explanation

anyone can understand in one

Submitted by Anonymous on Sat, 02/19/2011 - 03:03.

anyone can understand in one view. thanks . great work

great........................

Submitted by Anonymous on Tue, 02/22/2011 - 10:30.

great..................................

Great explanation thanks

Submitted by Anonymous on Wed, 02/23/2011 - 16:39.

Great explanation thanks

its useful for the beginners

Submitted by Anonymous on Fri, 02/25/2011 - 11:22.

its useful for the beginners .....

A wounderful example for this

Submitted by Anonymous on Fri, 03/04/2011 - 01:41.

A wounderful example for this newbie. Thanks!

Best Exampale

Submitted by Anonymous on Thu, 03/10/2011 - 06:51.

Best Exampale

Submitted by Anonymous on Thu, 03/10/2011 - 06:51.

Best Exampale

nice one

Submitted by Anonymous on Fri, 03/18/2011 - 14:14.

nice one

A holistic understanding into

Submitted by Anonymous on Mon, 03/28/2011 - 18:02.

A holistic understanding into the Hashtable concept.Thank you.

System.out.println("Hashtable

Submitted by Anonymous on Sat, 04/02/2011 - 00:38.

System.out.println("Hashtable does not contain One as value"); in line 88, that should say "does not contain One as a key" instead, correct?

good way to explain things

Submitted by Anonymous on Mon, 04/04/2011 - 13:16.

good way to explain things precisely

This tutorial is outdated now

Submitted by Anonymous on Wed, 04/06/2011 - 18:48.

This tutorial is outdated now you should add genericity to all the declarations that will allow you not to cast types everytime you want to use a value of the hashtable

Keep it up man good work.

Submitted by Anonymous on Sun, 04/10/2011 - 05:05.

Keep it up man good work.

thx, it is useful

Submitted by Anonymous on Tue, 04/19/2011 - 12:25.

thx, it is useful

thanxs good way to explain

Submitted by Anonymous on Wed, 04/27/2011 - 09:52.

thanxs good way to explain things Regards Ashok

Agree with Anonymous here,

Submitted by Anonymous on Mon, 05/02/2011 - 10:13.

Agree with Anonymous here, Java is now moved from java 4 to java5 and generic is a must known feature. you should update this post to allow generics here , any way good information for anyone new to hashmap. Javin How HashMap works in Java