Solved

Get both key and value from Hashtable element.

Posted on 2002-05-07
9
376 Views
Last Modified: 2010-03-31
I've got a Hashtable storing parameter data in a class I'm using for message passing. The key values used to index the hashtable will vary from instance to instance, as different messages will use different parameters (think of it like xml if that helps: <tag key="value" key="value">, where both the keys and values vary from tag to tag).

I need to iterate over the hashtable, extracting both the value *and* the key of each element contained therein.

The generic Iterator's next() method returns an object, which in the case of Hashtable I presume is the value section of the particlar element. The Object class contains a method int hashCode(), which seems to be something near what I'm after, except that an integer isn't of much use to me --  I need something I can extract a String key from.

How can I do this?
0
Comment
Question by:Subhuman
  • 4
  • 3
  • 2
9 Comments
 
LVL 9

Expert Comment

by:doronb
ID: 6993321
Hi,


Try this example:

     public static void iterateTable(Hashtable h) {
          if (h != null) {
               Iterator i = h.entrySet().iterator();
               while (i.hasNext()) {
                    Map.Entry me = (Map.Entry)i.next(); // Casting to Map.Entry is VERY IMPORTANT!!
                    Object key = me.getKey(); // The Key...
                    Object value = me.getValue(); // The Value..
                    // Now do something with the {key, value} pair...
               }
          }
     }

Do not forget to cast the key and value objects to whatever it is you need. I hope this helps..


Doron
0
 
LVL 92

Accepted Solution

by:
objects earned 300 total points
ID: 6993334
Hashtable ht = .....;

Enumeration i = ht.keys();
while (i.hasMoreElements())
{
   Object key = i.nextElement();
   Object value = ht.get(key);

   // Do what you want with your key and value
}
0
 
LVL 1

Author Comment

by:Subhuman
ID: 6993408
I like object's solution more; it's much cleaner.
0
Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

 
LVL 1

Author Comment

by:Subhuman
ID: 6993415
I've wrapped your code in a couple of classes, objects (I bet that name gets awfully ambiguous in detailed conversations ^_^).

Here's what I've got. It compiles and runs fine:

//======== HashEnumerator.java

import java.util.Enumeration;
import java.util.Hashtable;
public class HashEnumerator {
     private Enumeration e;
     private Hashtable ht;

     public static void main (String args[]) {
          Hashtable ht = new Hashtable ();
          ht.put ("one", new Integer (1));
          ht.put ("two", new Integer (2));
          ht.put ("three", new Integer (3));
          ht.put ("four", new Integer (4));
          ht.put ("five", new Integer (5));
          ht.put ("six", new Integer (6));

          HashEnumerator henum = new HashEnumerator (ht);
          while (henum.hasNext ()) {
               HashElement he = henum.next ();
               System.out.println ("Key: " + he.getKey () + "\tValue: " + he.getValue ());
          }
     }

     public HashEnumerator (Hashtable ht) {
          this.ht = ht;
          e = ht.keys ();
     }

     public boolean hasNext () {
          return e.hasMoreElements ();
     }

     public HashElement next () {
          Object k, v;
          if (e.hasMoreElements ()) {
               k = e.nextElement ();
               v = ht.get (k);
               return new HashElement (k, v);
          }
          else
               return null;
     }
}


//================= HashElement.java

import java.util.Hashtable;

public class HashElement {
     private Object key;
     private Object value;

     public HashElement (Object key, Object value) {
          this.key = key;
          this.value = value;
     }

     public Object getKey () {
          return key;
     }

     public Object getValue () {
          return value;
     }
}

=============================

Before I close this thread, can you spot any potential issues in there that will need addressing? It looks ok to me, but I haven't really used hashes much before so there might be something I'm missing.
0
 
LVL 92

Expert Comment

by:objects
ID: 6993445
Looks ok to me :)
0
 
LVL 1

Author Comment

by:Subhuman
ID: 6993510
Cool, thanks a lot. Enjoy the points. ^_^
0
 
LVL 92

Expert Comment

by:objects
ID: 6993525
Thanks mate :-)
Let me know if you have any problems.

http://www.objects.com.au
Brainbench MVP for Java 1
http://www.brainbench.com
0
 
LVL 9

Expert Comment

by:doronb
ID: 6993976
Hi,


Just tried to stick with your Iterator approach.


Doron
0
 
LVL 1

Author Comment

by:Subhuman
ID: 6995219
Heh, well thanks anyway. :)
0

Featured Post

Free Tool: IP Lookup

Get more info about an IP address or domain name, such as organization, abuse contacts and geolocation.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Title # Comments Views Activity
servlet example 11 49
jdbc error in jsp application 20 63
hibernate jars 4 45
CSV file parsing thru Java 13 34
By the end of 1980s, object oriented programming using languages like C++, Simula69 and ObjectPascal gained momentum. It looked like programmers finally found the perfect language. C++ successfully combined the object oriented principles of Simula w…
Java Flight Recorder and Java Mission Control together create a complete tool chain to continuously collect low level and detailed runtime information enabling after-the-fact incident analysis. Java Flight Recorder is a profiling and event collectio…
This tutorial covers a practical example of lazy loading technique and early loading technique in a Singleton Design Pattern.
This video teaches viewers about errors in exception handling.

792 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question