ThreadDemoCounter.java

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public class ThreadDemoCounter implements Runnable
{
    
    private static Lock lock = new ReentrantLock();
    private int counter;

    public int getCounter()
    {
        return counter;
    }

    public void incrementCounter()
    {
        counter++;
    }

    public static final int numLoops = 4;
    public static final int numPrints = 10;


    public ThreadDemoCounter()
    {
        counter = 0;
    }


    public void go() throws Exception
    {
        //Run the multithreaded demo a few times
        for (int foo = 0; foo < numLoops; foo++)
        {
            counter = 0; //reset

            Thread t1 = new Thread(this);
            Thread t2 = new Thread(this);
            t1.start();
            t2.start();
            t1.join();
            t2.join(); //wait for both
            System.out.println("===== end loop =====");
        }
    }

    public static void main(String[] args) throws Exception
    {
        ThreadDemoCounter t = new ThreadDemoCounter();
        t.go();
    }


    public void run()
    {
        lock.lock();
        for (int j = 0; j < numPrints; j++)
        {
            System.out.println("counter = " + getCounter());
            incrementCounter();
        }
        System.out.println();
        lock.unlock();
    }


}