Question

My question is why or how i can make “listenerList” value as 1 or 2, so that i can track and get status of that instance from alert class with the help of vector()? ex: listenerList is my process id to track them, but its always value of 0

Here is whole code, not working to see the output: “it WORKS!!!, if i can reach here!!!”:

[updated after suggestion, but still same, not working]

1) Interface

public interface Listener
{
    public void registered();
    public void connected(String IP,int Port);
    public void disconnected();
}

2) Interface extending

public class alert implements Listener
{
  public void  registered() 
  {System.out.println("it WORKS!!!, if i can reach here!!!"); System.exit(0);}
  public void connected(String IP, int Port) 
  { throw new UnsupportedOperationException("Not supported yet.");}
  public void disconnected() 
  {  throw new UnsupportedOperationException("Not supported yet.");   }
}

3) Main class to use

public class Provider extends Thread
{
  public Vector listenerList;
  public alert  alert;   

  public Provider(String userName) throws Exception{ listenerList = new Vector();   
    addListener(alert);
  }
  public void addListener(Listener ls)    {     listenerList.addElement(ls);}  
  public void removeListener(Listener ls) { listenerList.removeElement(ls); }  

  public void run()
  {
    while(running)
    {
      fireRegisteredEvent(); // shows now value of 1, but does not do exit(0);
    }
  }  

  private void fireRegisteredEvent() 
  {
      System.out.println("Fireing Registration: " + System.currentTimeMillis()); 
      System.out.println("Fireing Registration: " + listenerList.size());

      for (int i = 0; i < listenerList.size(); i++) 
      {              
          alert.registered();  
          System.exit(0);                  
      }

  }  
}

4) Action

private Provider multiinstance;
multiinstance = new Provider("Why are you not triggering: System.exit(0);??????");
multiinstance.start();

5) Output

Fireing Registration: 1303646370073
Fireing Registration: 1

….

6) Expecting result:

a) output: System.out.println("it WORKS!!!, if i can reach here!!!");
OR
b) listenerList.size() value is either 1 or 2?!!
OR
c) alert class and interface should react? no?? if not how i can ??

Answer 1

Because you never instantiated a listener and assigned it to one of the providers. In other words you never call addListener(...) and thus no listener can be triggered.