Sleep or wait() / notify() Which is better IYO

Question

Consider an app where a central object, like an information server is handed a query and an amount of time will pass before that information is available. For caching, many objects may ask the same question and be waiting on the same answer. Is it better to have the queries do a sleep loop to wait for the response or is it better for the queries to register with the server and call a wait(), then have the server issue a notify to objects that were waiting?
Thanks for the advice.

Answer 1

Thank you. I like sleep as well. Although with three little ones that can be a difficulty.
I am having a difficulty with how to implement the wait notify. Can you tell me if the following is a good / bad / normal / horribly wrong example?
// sorta code...
// This class goes to a central location
// or the network for an answer.  It represents one answer for one query.
class InfoServerQuery extends Thread{
  volatile boolean isComplete = false;
  volatile String response = null;
  Vector pool = new Vector();
  public synchronized boolean isReady(Object obj){
    if(!isComplete){
      // Add object to answer pool
      pool.add(obj);
      return false;
    }else{
      return true;
  public void run(){
    try{
      // Get the information.......
      response = getInfo();
      // set isComplete
      isComplete = true;
      // notify all that are waiting.
      for(int a = 0; a < pool.size(); a++)
      synchronized(pool.get(a)){pool.get(a).notify();};
    }catch(Exception e){
      throw new RuntimeException();
// This class asks the questions.
class QueryClient{
  // instantiated in constructor
  InfoServerQuery q;
  public String getAnswer() throws Exception{
    while(!q.isReady(this)) synchronized(this){wait();};
    return q.response;
}Thanks for any insights.