ConcurrentCounterSample.java

public class ConcurrentCounterSample {
	public static void main(String[] args) throws InterruptedException {
		final int NUM_THREADS = 2;

		MyCounter counter = new MyCounter();
		Thread[] threads = new Thread[NUM_THREADS];
		int i;

		long startTime = System.currentTimeMillis();

		for (i = 0; i < NUM_THREADS; i++) {
			Thread thread = new Thread(new CounterIncRunnable(counter));
			thread.start();
			threads[i] = thread;
		}

		System.out.println(i + " Threads started.");

		for (i = 0; i < NUM_THREADS; i++) {
			threads[i].join();
		}

		long stopTime = System.currentTimeMillis();
		long elapsedTime = stopTime - startTime;
		System.out.println("Elapsed Time: " + elapsedTime + " ms");
		System.out.println("Counter value: " + counter.value());
	}
}

class CounterIncRunnable implements Runnable {
	private MyCounter counter;

	public CounterIncRunnable(MyCounter counter) {
		this.counter = counter;
	}

	public void run() {
		for (int i = 0; i < 10000000; i++) {
			counter.increment();
		}
	}
}

class MyCounter {
	private int c = 0;

	/* Remove the synchronized keyword to run into race conditions */
	public synchronized void increment() {
		c++;
	}

	public int value() {
		return c;
	}
}