The Car Class

Car.java

package test.concurrency.traffic;

import java.util.concurrent.Callable;
import java.util.concurrent.atomic.AtomicInteger;

public class Car implements Callable<Car> {

  private static StopLight sLight = StopLight.getInstance(); // StopLight will
																// be injected
																// into Car
	private AtomicInteger pos; // Position of car before stop light

	final private String name;
	public String getName() {
		return name;
	}

	public Car(AtomicInteger pos, String name) throws IllegalArgumentException {
		super();
		if (pos.get() < 0 || pos.get() > Consts.PAVEMENT_LENGTH) {
			throw new IllegalArgumentException("Argument value not in range...");
		}
		this.name = name;
		this.pos = pos;
	}

	private void goAhead() { // Move car ahead on road by one unit
		try {
			Thread.sleep(Consts.ONE_SEC); // one unit per second
			pos.addAndGet(1);
		} catch (InterruptedException e) {
			Thread.currentThread().interrupt();
		}
	}

	public synchronized AtomicInteger getPos() {
		return pos;
	}

	@Override
	public Car call() {
		if (pos.get() > Consts.PAVEMENT_LENGTH / 2) { // Once car crosses the
			// StopLight, simply move it ahead till end of the Road
			while (getPos().get() != Consts.PAVEMENT_LENGTH) {
				goAhead();
			}
		} else {
			while (pos.get() != Consts.PAVEMENT_LENGTH) {
				synchronized (sLight) { // StopLight instance used as Object
				// monitor to make cars wait on signal until
				// notified by Road
					while (StopLight.getState() == LightState.RED
							&& pos.get() == Consts.PAVEMENT_LENGTH / 2) {
						try {
							sLight.wait(10 * Consts.ONE_SEC); // wait until Road
																// toggles
																// stoplight and
																// invokes
																// notify
						} catch (InterruptedException e) {
							Thread.currentThread().interrupt();
						}
					}
				}
				goAhead(); // Move car one unit ahead
			}
		}
		return this;
	}
}