notify() and wait() problem

[greyradio]

I've recently have been given an assignment to do and it seems that notify() does notify() any of the waiting threads. The project entails 10 commuters and two different toll booths. The EZPass booth allows a commuter to pass easily while a cash booth creates a wait line. The wait line is expected to wait for the 5th commuter to pass before any commuter on the wait line can pass through the toll booth. This is where my problem lies. All the commuters wait for the 5th commuter thread to pass, however when the 5th commuter does notify(), none of the commuter threads receive it. I've spend hours trying to solve this problem but I haven't has any results. Hopefully someone can point out what I'm doing wrong with the synchronized method. I've attached the java files. Thanks.

Here is the output, most of the time, :

Commuter 0 has entered the boulevard. He entered lane : 0 at time: 1
Commuter 0 has entered the bridge at time : 1
Commuter 0 will pay cash.
Commuter 0 is entering the toll booth line. Time: 1
Commuter 0 Entered the toll booth. Value is: 0
Commuter 0 Entered the waiting line. Value is: -1
Commuter 0 Will wait now.
Commuter 2 has entered the boulevard. He entered lane : 2 at time: 1
There are double-parked cars in Commuter 2 lane. Time: 1
Commuter 2 is yielding until lane is clear.Time:2
Commuter 4 has entered the boulevard. He entered lane : 1 at time: 2
Commuter 4 has entered the bridge at time : 2
Commuter 4 will pay cash.
Commuter 4 is on a high speed chase. He will speed right through the cash booth. Time: 2
Commuter 4 Entered the toll booth. Value is: -1
Commuter 4 Exited the line. Value: -1
Commuter 4 notifiying the next waiter. Value: 0
Commuter 4 has been caught and placed in jail. Time: 2
The value on the toll is 0
Commuter 6 has entered the boulevard. He entered lane : 2 at time: 2
There are double-parked cars in Commuter 6 lane. Time: 2
Commuter 6 is yielding until lane is clear.Time:2
Road Rage from Commuter 2. Speeding to get to work on time. Time: 2
I must stop since I'm nearing a red light, thinks Commuter 2.
Commuter 2 has entered the bridge at time : 2
Commuter 2 has an EZPass.
Commuter 2 has left the bridge and will head to work.
Commuter 2 has arrived at work. Time: 4
Commuter 1 has entered the boulevard. He entered lane : 2 at time: 4
Road Rage from Commuter 6. Speeding to get to work on time. Time: 4
I must stop since I'm nearing a red light, thinks Commuter 6.
Commuter 6 has entered the bridge at time : 4
Commuter 6 will pay cash.
Commuter 6 is entering the toll booth line. Time: 4
Commuter 6 Entered the toll booth. Value is: 0
Commuter 6 Entered the waiting line. Value is: -1
Commuter 6 Will wait now.
Commuter 8 has entered the boulevard. He entered lane : 0 at time: 4
Commuter 8 has entered the bridge at time : 4
Commuter 8 has an EZPass.
Commuter 8 has left the bridge and will head to work.
Commuter 8 has arrived at work. Time: 5
There are double-parked cars in Commuter 1 lane. Time: 4
Commuter 1 is yielding until lane is clear.Time:5
Road Rage from Commuter 1. Speeding to get to work on time. Time: 5
I must stop since I'm nearing a red light, thinks Commuter 1.
Commuter 1 has entered the bridge at time : 5
Commuter 1 has an EZPass.
Commuter 1 has left the bridge and will head to work.
Commuter 1 has arrived at work. Time: 5
Commuter 3 has entered the boulevard. He entered lane : 0 at time: 5
Commuter 3 has entered the bridge at time : 5
Commuter 3 has an EZPass.
Commuter 3 has left the bridge and will head to work.
Commuter 3 has arrived at work. Time: 6
Commuter 5 has entered the boulevard. He entered lane : 0 at time: 6
Commuter 5 has entered the bridge at time : 6
Commuter 5 has an EZPass.
Commuter 5 has left the bridge and will head to work.
Commuter 5 has arrived at work. Time: 6
Commuter 7 has entered the boulevard. He entered lane : 1 at time: 6
Commuter 7 has entered the bridge at time : 6
Commuter 7 has an EZPass.
Commuter 7 has left the bridge and will head to work.
Commuter 7 has arrived at work. Time: 7
Commuter 9 has entered the boulevard. He entered lane : 2 at time: 7
There are double-parked cars in Commuter 9 lane. Time: 7
Commuter 9 is yielding until lane is clear.Time:7
Road Rage from Commuter 9. Speeding to get to work on time. Time: 7
I must stop since I'm nearing a red light, thinks Commuter 9.
Commuter 9 has entered the bridge at time : 7
Commuter 9 has an EZPass.
Commuter 9 has left the bridge and will head to work.
Commuter 9 has arrived at work. Time: 7

The threads are created and stored in an array in the main method of the Project 1 class. And here is my synchronized method:

 
synchronized void tollBooth(){
 System.out.println(Thread.currentThread().getName() +
        " Entered the toll booth. Value is: " + value);
 if(commuterNumber !=4){
    value --;
    if(value <0){
            System.out.println(Thread.currentThread().getName() +
                " Entered the waiting line. Value is: " + value);
        while(true){
            try{
                System.out.println(Thread.currentThread().getName()+ 
                        " Will wait now.");
               wait();
 
          System.out.println(Thread.currentThread().getName() +
               " is breaking out the while.");
              break;
       }catch(InterruptedException e){
           if(value >= 0) 
               break;
           else continue;
                    }
                }
            }
        }
   System.out.println(Thread.currentThread().getName()+
           " Exited the line. Value: "+ value);
   value++;
    if(value <= 0){
       System.out.println(Thread.currentThread().getName() +
           " notifiying the next waiting thread. Value:  "+ value);
                 notify();
            }
 
        }
 
 
 

[JosAH]

I suspect you're synchronizing on the wrong object(s). A synchronized method synchronizes on the object for which the method is a member. If you have 10 different objects they synchronize on these 10 different objects; if they enter a wait state no other thread can notify them because all threads synchronized on a different object. Also have a look at the java.utils.concurrent package which has many handy classes and methods available (pay special attention to the Semaphore class).

kind regards,

Jos

[greyradio]

Thanks I see what I was doing wrong. It works now.