Why my synchronized method not working properly?

Question

I have this synchronized method that prints counter, I have 4 Threads so I am expecting final value of my counter to be 400000 as my counter is a static variable.

but every time I run my code, it is giving me different values of counter.

Following is my code:

class MyThread implements Runnable{

    private static int counter=1;
    @Override
    public void run() {
        try {
            this.syncMethod();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
    public synchronized void syncMethod() throws InterruptedException{
        for(int i=0;i<100000;i++){
            System.out.println(Thread.currentThread().getName()+" : "+counter++);
        }
    }
}

public class MyController {
    public static void main(String[] args) throws InterruptedException {
        Runnable r1=new MyThread();
        Runnable r2=new MyThread();
        Runnable r3=new MyThread();
        Runnable r4=new MyThread();
        Thread t1;
        Thread t2;
        Thread t3;
        Thread t4;
        t1=new Thread(r1,"Thread 1");
        t2=new Thread(r2,"Thread 2");
        t3=new Thread(r3,"Thread 3");
        t4=new Thread(r4,"Thread 4");

        t2.start();
        t1.start();
        t3.start();
        t4.start();
    }
}

Answer 1

The variable is static, but the method that you synchronized is not static. This means that it will acquire the monitor on the current instance, and every thread has a different current instance.

A simple solution is to make the syncMethod method static as well; in that case, it will take a lock on the monitor that is shared by all instances of the MyThread class:

public static synchronized void syncMethod()