crazyStart crazyStart - 1 month ago 11
Java Question

Print odd & even number using Multi threading

I am trying to learn Multi threading and for practice, I am trying to print odd & even number using two thread. I have created an object which will act as a lock for the both the threads. When I try to execute it throws

java.lang.IllegalMonitorStateException
.

class EVENODDimpl implements Runnable {
int num;
int temp = 0;
Object lock = new Object();

public EVENODDimpl( int num) {
this.num = num;
}

public void run() {
try {
synchronized (lock) {
while(temp<num) {
temp++;
System.out.println(Thread.currentThread().getName()+" "+temp);
this.notify();
this.wait();
}
}
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}


Main Method:

public class EVENODD {
public static void main(String[] args) {
int i = 10;
EVENODDimpl ei = new EVENODDimpl(i);
Thread t1 = new Thread( ei,"EvenThread");
Thread t2 = new Thread( ei,"OddThread");
t1.start();
t2.start();
try {
t1.join();
t2.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}

Answer Source

You wait and notify on this, but you should wait and notify on lock because you synchronize on lock, you can't wait and notify on other object than the one on which you're synchronizing, working version:

class EVENODDimpl implements Runnable {
    int num;
    int temp = 0;
    Object lock = new Object();

    public EVENODDimpl( int num) {
        this.num = num;
    }

    public void run() {
        try {
            synchronized (lock) {
                while(temp<num) {
                    temp++;
                    System.out.println(Thread.currentThread().getName()+"   "+temp);
                    lock.notify();
                    lock.wait();
                }
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        } 
    }
}