threads synchronization problem

[Abhay Saini]

class Q {
int n;
boolean sse = false;
synchronized int get(){
    while (!sse)
        try{
            wait();
        }catch(InterruptedException e){
            System.out.println("Interrupted Exception Caught");
        }
    System.out.println("Got :" + n);
    sse = false;
    notify();
    return n;
        }
synchronized void put(int n){
    while(sse)
        try{
            wait();
        }catch(InterruptedException e){
         System.out.println("Caught");
        }
    this.n = n;
    sse = true;
    System.out.println("Put :" + n);
    notify();
}

}
class Producer implements Runnable{
    Q q;
    Producer(Q q) {
        this.q = q;
        new Thread(this, "Prodcuer").start();
    }
    public void run(){
        int i = 0;
        while(true) {
        q.put(i++);
        }
    }
}
class Consumer implements Runnable{
    Q q;
    Consumer(Q q) {
        this.q = q;
        new Thread(this, "Consumer").start();
    }
    public void run(){

        while(true) {
        q.get();
        }
    }
}
public class Main {

  
    public static void main(String[] args) {
  Q q = new Q();
  new Producer(q);
  new Consumer(q);
  System.out.println("Press Control C to stop");
    }

}

I have 2 questions.

Q1. now the definition of wait() function is like this : tells the calling thread to give up monitor and go to sleep until some other thread enters the same monitor and calls notify().
Now in this program two threads(One related to consumer and one to producer) use the same object q in get and put respectively. So is there only one monitor existing for the object q, which is entered when any thread uses a function involving q?

Q2 Here the Consumer waits until Producer notifies it, but the Producer also waits until the consumer notifies it? Who starts first?
In the output, Producer comes first but how?

[Jesper de Jong]

Please be forthright when crossposting to other sites.

[Abhay Saini]

I posted this at Stackoverflow.com too
But i want to know as many opinions as possible.
Sorry if anyone is offended.
I will tell if I like any answer at that site so that your time is not wasted

[Abhay Saini]

I got the 2nd question
but not the first one?

[Jesper de Jong]

Abhay Saini wrote:I posted this at Stackoverflow.com too
But i want to know as many opinions as possible.

No problem, but when you do that, please say that you've also posted it somewhere else and include a link, so that people don't have to waste time answering the question when it has already been answered somewhere else.

[Dennis Grimbergen]

Jesper de Jong wrote:
No problem, but when you do that, please say that you've also posted it somewhere else and include a link, so that people don't have to waste time answering the question when it has already been answered somewhere else.

Well that is ofcourse what he wants. If you post a question at several places on the net then you get some responses. If 2 or more people give the same response while they respond to a message on a different forum, then these responses have some value.

I understand that for some more basic things this is not necessary and desirable, but if the question is more advanced these equal responses would give me a good feeling to look in such direction...

[Haiti Meid]

Jesper de Jong wrote:Please be forthright when crossposting to other sites.

I think that's his right. I got no problem with that.

@Abhay: Can you try this?

class Q {

  int n;
  boolean hasData = false;

  synchronized int get(){
    //wait if no data available
    if (!hasData)
      try{
        wait();
      }catch(InterruptedException e){
        System.out.println("get() wait interrupted");
      }
    System.out.println("Got :" + n);
    hasData = false;

    //resume put()
    notify();
    return n;
  }

  synchronized void put(int n){
    this.n = n;
    hasData = true;
    System.out.println("Put :" + n);

    //let get() handles data
    notify();

    //wait while get() is handling data
    try {
      wait();
    } catch(InterruptedException e){
      System.out.println("put() wait interrupted");
    }
  }

}

class Producer implements Runnable{

  Q q;
  int max;

  Producer(Q q, int max) {
    this.q = q;
    this.max = max;
    System.out.println("Producer's starting...");
    new Thread(this, "Prodcuer").start();
  }

  public void run(){
    int i = 0;
    while (true) {
      q.put(i++);
      if (i > max) {
        q.put(-1);
        break;
      }
    }

    System.out.println("Procuder stops!");
  }

}

class Consumer implements Runnable{

  Q q;
  
  Consumer(Q q) {
    this.q = q;
    System.out.println("Consumer's starting...");
    new Thread(this, "Consumer").start();
  }

  public void run(){
    while (true) {
      //breaks if data received < 0
      if (q.get() < 0)
        break;
    }

    System.out.println("Consumer stops!");
  }

}

public class Main {
  
  public static void main(String[] args) {
    Q q = new Q();

    //note: try creating consumer first...
    new Consumer(q);
    //create new producer, let it counts from 0 to 5
    new Producer(q, 5);
  }

}

I renamed "sse" to "hasData" in order to make it more clear:
+ consumer waits for data.
+ producer puts data in, then notify(), and waits for consumer.
+ consumer handles the data, then notify().
+ procedure ends.