What is wrong with my thread condition??

Question

I have two kinds of threads:
1) WriterThread is cable of inserting keys with a corresonding object into a database.
2) ReaderThread which should be able to wait for a specific key is inserted into the database.
I store the key waited for by a ReaderThread and its id in a HashTable (the database is also a Hashtable).
If I have 3 ReaderThreads that is waiting (with id 1,2,3) and thread 2 is waiting for "key2", I would only have ReaderThread 2 to wake up when "key2" is inserted by a WriterThread.
Therefor I have made a condition in the "waitfor" method for the threads that is awakened (its after the first call to wait()). But it only works the first time I insert one of the keys awaited keys. The next time I insert a key all the remaining threads are reactivated!
public class DataBase extends Hashtable{
    private Vector thread_vector; // The vector that contains all the threads.
    private Hashtable hold = new Hashtable(); // Holds the id and the key the thread is waiting for.
    private int t_id = 0; // The id of the thread that gets updated each time insert is called.
    public DataBase(Vector v){
        thread_vector = v;
    public void findId(Object k){
        int q = ((Integer) k).intValue();
        t_id = q; // Here t_id is set to the very id of the thread that is waiting for the newly inserted key.
    public synchronized void insert(String key, String o){
        if (this.containsKey(key)){
            System.out.println("Database already contains key: \""+ key + "\".");
        else{
            if (hold.containsKey(key)){
                this.findId(hold.get(key));
                hold.remove(key); // The key that has been waited for is deleted from the waiting queue array.
                System.out.println("Key: \"" + key +"\" inserted");
                this.put(key,o);
                notifyAll();
            else{
                this.put(key,o);
                System.out.println("Key: \"" + key +"\" inserted.");
    public synchronized void delete(String key){
        this.remove(key);
        System.out.println("Key: "+"\"" + key + "\" with its corresponding value is removed from the Database." );
    public synchronized void waitfor(String key, int id){
        Integer thread_id = new Integer(id);
        hold.put(key,thread_id);
        try{
            wait();
        catch(InterruptedException e){}
        // This is where the problem is and where all the awakened threads battle to get inside the monitor!!
        if (Thread.currentThread() == thread_vector.get(t_id)){
            System.out.println("The right thread is awakened");
        else{
            try{
                System.out.println("Return to wait");
                wait();
            catch(InterruptedException e){}
}

Answer 1

Well, when it checks if the key is in the hold table, if it is then 'notifyAll()' notifies all threads!
Try this, instead if an int to identify the threads, try using a monitor, that way instead of 'notifyAll()' you could use:
((Thread)hold.get(key)).notifyAll()Then only the thread that is registered for that key get's notified.
and in the waitFor method use:
    public synchronized void waitfor(String key, Object id){
        Integer thread_id = new Integer(id);
        hold.put(key,thread_id);
        try{
            id.wait();
            }