Vector as a HashMap key

It'll work. Here's some code that follows. However, in my sample, I'd rather store 'user' as the key to the HashMap. Also, the code below won't allow for the list to be sorted or anything after it is added to the HashMap.

import java.util.*;

public class VectorAndHashMap

{

static class Preference

{

String color;

String fontSize;

public Preference(String _color, String _fontSize) {

color=_color;

fontSize=_fontSize;

}

public String toString() {

return color+"/"+fontSize;

}

}

public static void main(String[] args)

{

Object[] users = {"smith", "brown", "jones"};

// create the Vector

Vector v = new Vector(Arrays.asList(users));

Object[] prefs = { new Preference("blue", "big"),// smith's

new Preference("blue", "small"),// brown's

new Preference("red", "medium") }; // jones's

// create the HashMap

HashMap hashmap = new HashMap();

// load the HashMap

for(int i=0; i<v.size(); i++)

hashmap.put(new Integer(i), prefs[i]);

// lookup index for "brown"

int j=0;

boolean found = false;

for(j=0; j><v.size(); j++) {

String user = (String)v.get(j);

if(user.equals("brown")) {

found = true;

break;

}

}

// retrieve record

if(found) {

Preference pref = (Preference)hashmap.get(new Integer(j));

System.out.println("brown's record: " + pref);

}

}

}

>

CWalker807 at 2007-6-29 17:42:50 >

> Thanks for your reply! And it is helpful for me.

> However, when the vector is full and it changed it's

> size, will the hashmap still has correct key? Since I

> don't know whether the vector size change will casue

> what result to the hashmap.

I'm not sure if it will work or not (I suspect not) since it was pointed out that you can't sort the Vector afterwards.

You also need to realize that this isn't very efficient since the hash routine will need to use the object to generate its actual key value. If you really need to do this, I would recommend that you derive from Vector and provide a method to generate a key value. You do this by implementing your own public int hashCode()

method, overriding the inherited one (from Object). This should allow you to modify the Vector in any way you want, so long as the returned hashCode is in no way dependent on the contents of the Vector itself.

sage_sam at 2007-6-29 17:42:50 >

I use hashmap to store data between the vector of User object in DB, and the vector of User name in list. So I need to do a mapping between list and the object in DB, in order to perform a del function, which can erase the user in the list and DB at same time. The list is only showing the name of users. But it is not the primary key of DB, so it is diffcult for me to del it in DB by just choosing the name in the list.

alvamak at 2007-6-29 17:42:50 >