Hashtables and Vectors

Question

Hi there !!!
Today I made some stuff but still a lot more needs to be done.
So first of all let me explain what is all about.
I have to make a hashtable that contains a String as a key and a vector as a value associated with that String.The following classes extend Relation (this is an interface)
Analogy,Cause and so on.
The instances have as fields DestinationID and SourceID .
The table sorts the instances as follows : the objects with the same SourceID are put in a vector that is mapped to that SourceID.There is a second table that does the same but for the DestinationID-s
The tables I have implemented recursively
Here is the code for one of them:
public class AnnotationThread1 {
    private Vector v = new Vector();
    private Hashtable h_sourceID = new Hashtable();
    private Hashtable h_destinationID = new Hashtable();
    private Vector leaves = new Vector();
/** Creates a new instance of AnnotationThread1 */
    public AnnotationThread1() {}
/** Creates the hashtable (recursively) the key is the SourceID and the
*value is a vector that contains all the nodes that have the same SourceID
    public Hashtable add(Relation r){
        String sourceID = r.getSourceID();
        Vector v = (Vector) h_sourceID.get(sourceID);
        //if the Vector is null we create a new one
         if (v == null) v = new Vector();
        //if we add the same node twice the second will be neglected
          if (!v.contains(r)){
           v.add(r);
           h_sourceID.put(sourceID,v);
      return h_sourceID;
    }Now i should also retrieve the so called leaves : here the ID -s that are not SourceID -s . (they are not parents so to say).I have done that for every single object (i chech whether the given Relation possesses a leaf or not) but still I can not come up with an idea how to retrieve all leaves and for example to have them in a vector .
Here is the code how I check if one ID is a leaf or not:
/** Asks if a given ID is a leaf or not(uses the add() method)
*@param Relation r
*@return false if the node does not have a leaf and true otherwise
    public boolean ifLeaf(Relation r){
      boolean ifleaf = false;
      String leaf = r.getDestinationID();
      if (!h_sourceID.containsKey(leaf)){ ifleaf = true; }
      return ifleaf;
    }If anyone has ideas I will be very glad.
The same problems I have with finding the root.
Thanks in advance...

Answer 1

OPS I forgot to mention how is the table actually created.Well in the main class i have something like:
public static void main(String args[]){
      AnnotationThread1 example = new AnnotationThread1();
      BackgroundInformation a = new BackgroundInformation(0.1f,0.3f,"a","b");
      example.add(a);
      Analogy b = new Analogy(0.2f,0.1f,"a","c");
      example.add(b);
      SupportArgument c = new SupportArgument(0.2f,0.1f,"b","d");
      example.add(c);The Strings are as mentioned the SourceID and the DestinationID.
for example after writing
System.out.printlnexample.add(c);I will get as an output(in NetBeans):
a=[collate.AnnotationThread.BackgroundInformation@1f12c4e,    collate.AnnotationThread.Analogy@93dee9]}