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sorting hashtable, need explaination

Posted on 2004-10-09
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Last Modified: 2010-03-31
I have seen a bunch of code to do this, but I am really confused on why things are implemented. Could someone give me the right way to sort hashtable by keys, if my key is a double and my value is  string... and provide explanation.

Is there anything like for Hashtable h;
h.sortbyKey();
???
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Question by:polkadot
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11 Comments
 

Author Comment

by:polkadot
ID: 12267003
or how to enumerate the hash table, by key. I understand the concept of enumeration, just not the code in java. Thanks.
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Expert Comment

by:sudhakar_koundinya
ID: 12267027
Can you explain why you need to sort Hashtable()??
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Expert Comment

by:sudhakar_koundinya
ID: 12267043
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Accepted Solution

by:
sudhakar_koundinya earned 500 total points
ID: 12267046
import java.util.Hashtable;
import java.util.Vector;
import java.util.Collections;
import java.util.Enumeration;


public class SortHashtable {

  public static void main(String[] args) {
    // Create and populate hashtable
    Hashtable ht = new Hashtable();
    ht.put("ABC", "abc");
    ht.put("XYZ", "xyz");
    ht.put("MNO", "mno");
   
    // Sort hashtable.
    Vector v = new Vector(ht.keySet());
    Collections.sort(v);
   
    // Display (sorted) hashtable.
    for (Enumeration e = v.elements(); e.hasMoreElements();) {
      String key = (String)e.nextElement();
      String val = (String)ht.get(key);
      System.out.println("Key: " + key + "     Val: " + val);
    }
  }
}
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Expert Comment

by:sciuriware
ID: 12267051
You can enumerate a Hashtable by means of an Iterator (to travel along all stored keys).
If you want to sort the contents you better transfer the contents to a TreeSet.
;JOOP!
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Expert Comment

by:sudhakar_koundinya
ID: 12267068
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Author Comment

by:polkadot
ID: 12267070
I guess I'm not really sorting, I just want to be able to retrieve the items of the hashtable in the numerical order of the keys
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Author Comment

by:polkadot
ID: 12267098
yeah I think your first answer is what I want ... was hoping for a bit more explanation of the code, but its ok.
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Expert Comment

by:sciuriware
ID: 12267102
Well a HashTable is optimised for retrieval speed, so it isn't sorted.
And thus you must sort the contents in order to do what you want.
;JOOP!
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Expert Comment

by:sudhakar_koundinya
ID: 12267157
>>was hoping for a bit more explanation of the code, but its ok.

1.First that code gets the keys as Set
2. Converts the Set to Vector.
3. Sort the Vector using Collections.sort(List)
4. Traverse the Hashtable using Sorted keys

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Expert Comment

by:sciuriware
ID: 12267176
As you can see I work on a very slow line.
;JOOP!
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