.java

public class Worker {
	Random random = new Random();
	private List<Integer> list1 = new ArrayList<Integer>();
	private List<Integer> list2 = new ArrayList<Integer>();
	/*if we were to try to make this synchronized, it will work, however, it will take twice as long 
	 * therefore, the second thread must wait for the same thread to finish before it can access these stages
	 */
	
	public synchronized void stageOne() throws InterruptedException {
		Thread.sleep(1);
		list1.add(random.nextInt(100));
	}

	public synchronized void stageTwo() throws InterruptedException {
		Thread.sleep(1);
		list2.add(random.nextInt(100));

	}

	public void process() {
		try {
			for (int i = 0; i < 1000; i++) {
				stageOne();
				stageTwo();
			}

		} catch (InterruptedException e) {
			e.printStackTrace();
		}
	}

	public void main() {
		System.out.println("Starting...");
		long start = System.currentTimeMillis();
		Thread thread=new Thread(new Runnable(){

			@Override
			public void run() {
				process();
				
			}
		});
		Thread thread1=new Thread(new Runnable(){

			@Override
			public void run() {
				process();
				
			}
		});
		//ArrayLists are not thread safe, therefore, they can interleave
		thread.start();
		thread1.start();
		try {
			thread.join();
			thread1.join();
		} catch (InterruptedException e) {
			e.printStackTrace();
		}
		long finish = System.currentTimeMillis();
		System.out.println("Time Taken " + (finish - start));
		System.out.println("List 1 Size " + list1.size());
		System.out.println("List 2 Size " + list2.size());

	}

}