Sorting of hashtables in a vector

[Mike Anna]

Hello,

I am looking at some code which sets a collection of hashtables (which should have been beans), into a vector, and that vector being moved around. Now there is a need to make sure the hashtables in the vector are sorted, based on any parametric value that is a part of the keys of the hashtable. I am trying to revisit some code and was able to come up with this,havent been able to test it though, I had read somewhere that comparing the hashcode values should help. I am not sure if the below is correct. Would this be the best approach ? Could you please help me with this one ?

	Vector toBeSorted = new Vector();
	for(int i=0;i<10;i++)
	{
		Hashtable ht = new Hashtable();
		ht.put("Name","A"+i);
		ht.put("Age", "21"+i);
		ht.put("Salary","1"+i);
		
		toBeSorted.add(ht);
	}
	
	
	//converting vector to list, so it can be sorted. 
	List l = new ArrayList(toBeSorted);

//sort before vector can be passed around
	
	Collections.sort(l, new Comparator() {
		public int compare(Object o1, Object o2) {
			return ((Vector) o1).get("Name").hashCode() - (Vector)o2.get("Name").hashCode());
		}
}    

cheers,

[Paul Clapham]

No, that wouldn't be the best approach. You are ordering the entries by their hashcodes if you do that, and the hashcodes are unpredictable random numbers. Which I don't think you want to use to sequence them.

If you want to sort on this "parametric value", whatever that is, then get the "parametric values" for each of the entries and just return "a.compareTo(b)" in your Comparator's method.

[Mike Anna]

Thanks for your input.

The only part that I am not able to understand is, how the sort method (with the comparator being passed) spin the loop ?
For ex: I did this :

   
//added the elements from a vector to an arraylist...
for(int i=10;i>1;i--)
	{
		Hashtable ht = new Hashtable();
		ht.put("Name","A"+i);
		ht.put("Age", "21"+i);
		ht.put("Salary","1"+i);
		
		toBeSorted.add(ht);
		
	}
	
	Enumeration ew = toBeSorted.elements();
	List l = new ArrayList(toBeSorted);
	while(ew.hasMoreElements()){
		System.out.println(">>>>1111");
//		System.out.println(ew.nextElement());
		l.add(ew.nextElement());
	}


//now trying to sort the hashtables in the arraylist based on the keys which are in the hashtable (based on which 'parameter', the sorting should happen. 
//For ex: can be age, name, sal. 

	Collections.sort(l, new Comparator(){
		 
        public int compare(Object o1, Object o2) {
            Hashtable p1 = (Hashtable) o1;
            Hashtable p2 = (Hashtable) o2;
            
           return p1.get(i)/* how would the looping happen ...unclear road begins*/.getName().compareTo(p2.getKey(...)getName());
        }

    });

For ex. here, I get the key based on the enumeration I retrieve. But how would that happen in the above sort ?

   

 Enumeration e = table.keys();
    while (e.hasMoreElements()) {
      String key = (String) e.nextElement();
      System.out.println(key + " : " + table.get(key));
    }

Id be glad for any pointers.

cheers,