The Java implementation of producer consumer throws Java lang.IllegalMonitorStateException

import java.util.LinkedList;

import java.util.LinkedList;
import java.util.Queue;

class Producer extends PubSub implements Runnable{

    @Override
    public void run() {
        synchronized(queue){
            if (queue.size() == 99){
                try { 
                    wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
            queue.add(2);
            try{
                Thread.sleep(1000);
            }
            catch (InterruptedException e){
                e.printStackTrace();
            }
            notify();
            }
        }       
}


class Consumer extends PubSub implements Runnable{

    @Override
    public void run() {
        synchronized(queue){
            if(queue.isEmpty()){
                try {
                    wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }   
            }
            System.out.println(queue.poll());
        }

    }

}
public class PubSub {
    static Integer QUEUE_SIZE = 100;
    Queue<Integer> queue = new LinkedList<Integer>();
    public static void main(String[] args) {
        Producer producer = new Producer();
        Consumer consumer = new Consumer();
        Thread producerThread = new Thread(producer);
        Thread consumerThread = new Thread(consumer);
        producerThread.start();
        consumerThread.start();
        System.out.println("Started both the threads");
    }

}

I get Java. Net in the wait () section lang.IllegalMonitorStateException. I want to know what I did wrong here Any ideas??

The complete exceptions I get are as follows

Exception in thread "Thread-1" Started both the threads
java.lang.IllegalMonitorStateException
    at java.lang.Object.wait(Native Method)
    at java.lang.Object.wait(Object.java:502)
    at Consumer.run(PubSub.java:36)
    at java.lang.Thread.run(Thread.java:745)
Exception in thread "Thread-0" java.lang.IllegalMonitorStateException
    at java.lang.Object.notify(Native Method)
    at Producer.run(PubSub.java:23)
    at java.lang.Thread.run(Thread.java:745)

Solution

I think my code works properly

As described in JB nizet, you must call wait and notify on the queue object I think such @ r_ 419_ 1829 @ is static for producer and consumer to share

I have included the while loop, and the code continues to run until the end of time

In addition, additional notification is required before producer and consumer wait for the first time

The following code contains the following changes:

import java.util.LinkedList;
import java.util.Queue;

class Producer extends PubSub implements Runnable{

    @Override
    public void run() {
         int index = 0;

         while (true) {
            synchronized(queue){
                while (queue.size() == QUEUE_SIZE){
                    try {
                        System.out.println("Producer waits");
                        queue.notify();
                        queue.wait();
                    } catch (InterruptedException e) {
                       e.printStackTrace();
                    }
                }

                System.out.println("Produce element " + (++index));
                queue.add(2);
                queue.notify();

                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e){
                    e.printStackTrace();
                }


            }
        }
    }
}


class Consumer extends PubSub implements Runnable{

     @Override
     public void run() {
         while (true) {
             synchronized(queue) {

                while (queue.isEmpty()){
                    try {
                         System.out.println("Consumer waits");
                         queue.notify();
                         queue.wait();
                    } catch (InterruptedException e) {
                         e.printStackTrace();
                    }
                }

                System.out.println("Consume element " + queue.poll());
                queue.notify();

            }
         }

     }

  }

public class PubSub {
     static Integer QUEUE_SIZE = 100;

     static Queue<Integer> queue = new LinkedList<Integer>();

     public static void main(String[] args) {
          Producer producer = new Producer();
          Consumer consumer = new Consumer();

          Thread producerThread = new Thread(producer);
          Thread consumerThread = new Thread(consumer);

          producerThread.start();
          consumerThread.start();

          System.out.println("Started both the threads");
     }

 }