仿真[汽车制造]
class Car{private final int id;private boolean engine = false,driveTrain = false,wheels = false;public Car(int idn){id = idn;}public Car(){id = -1;}public synchronized int getId(){return id;}public synchronized void addEngine(){engine = true;}public synchronized void addDriveTrain(){driveTrain = true;}public synchronized void addWheels(){wheels = true;}public synchronized String toString(){return "Car " +id +"[ engine: " + engine+ " driveTrain: " + driveTrain + " wheels: "+ wheels+ " ]";}}class CarQueue extends LinkedBlockingQueue<Car>{}class ChassisBuilder implements Runnable{private CarQueue carQueue;private int counter = 0;public ChassisBuilder(CarQueue cq){carQueue =cq;}public void run(){try {while(!Thread.interrupted()){TimeUnit.MILLISECONDS.sleep(500);Car c = new Car(counter++);System.out.println("ChassisBuilder created " +c);// Insert into queuecarQueue.put(c);}} catch (InterruptedException e) {System.out.println("Interrupted: ChassisBuilder");}System.out.println("ChassisBuilder off");}}class Assembler implements Runnable{private CarQueue chassisQueue, finishingQueue;private Car car;private CyclicBarrier barrier = new CyclicBarrier(4);private RobotPool robotPool;public Assembler(CarQueue cq, CarQueue fq, RobotPool rp){chassisQueue = cq;finishingQueue = fq;robotPool = rp;}public Car car(){return car;}public CyclicBarrier barrier(){return barrier;}public void run(){try {while(!Thread.interrupted()){// Blocks until chassis is available;car = chassisQueue.take();// Hire robots to perform work;robotPool.hire(EngineRobot.class, this);robotPool.hire(DriveTrainRobot.class, this);robotPool.hire(WheelRobot.class, this);barrier.await();// Unitl the robots finish// Put car into finishedQueue for futher workfinishingQueue.put(car);}} catch (InterruptedException e) {System.out.println("Exiting Assembler via interrupt");} catch (BrokenBarrierException e) {// This one we want to know aboutthrow new RuntimeException(e);}System.out.println("Assembler off");}}class Reporter implements Runnable{private CarQueue carQueue;public Reporter(CarQueue cq){carQueue = cq;}public void run(){try {while(!Thread.interrupted()){System.out.println(carQueue.take());System.out.println();}} catch (InterruptedException e) {System.out.println("Exiting Reporter via interrupt");}System.out.println("Reporter off");}}abstract class Robot implements Runnable{private RobotPool pool;public Robot(RobotPool p){pool = p;}protected Assembler assembler;public Robot assignAssembler(Assembler assembler){this.assembler = assembler;return this;}private boolean engage = false;public synchronized void engage(){engage = true;notifyAll();}// The part of run() that's different for each robot;abstract protected void performService();public void run(){try {powerDown();// Wait unitll neededwhile(!Thread.interrupted()){performService();assembler.barrier().await();// Synchronized// We're done with that job...powerDown();}} catch (InterruptedException e) {System.out.println("Exiting "+ this+ " via interrupt");} catch (BrokenBarrierException e) {// This one we want to know aboutthrow new RuntimeException(e);}System.out.println(this +" off");}private synchronized void powerDown() throws InterruptedException{engage = false;assembler = null; // Disconnet from the Assembler;// Put ourserlves back in the available pool;pool.release(this);while(engage == false)// Power downwait();}@Overridepublic String toString() {return getClass().getName();}}class EngineRobot extends Robot{public EngineRobot(RobotPool pool){super(pool);}protected void performService(){System.out.println(this +" installing engine");assembler.car().addEngine();}}class DriveTrainRobot extends Robot{public DriveTrainRobot(RobotPool pool){super(pool);}protected void performService(){System.out.println(this+" installing DriveTrain");assembler.car().addDriveTrain();}}class WheelRobot extends Robot{public WheelRobot(RobotPool pool){super(pool);}protected void performService(){System.out.println(this + " installing Wheels");assembler.car().addWheels();}}class RobotPool{// Quietly prevents identical entries;private Set<Robot> pool = new HashSet<Robot>();public synchronized void add(Robot r){pool.add(r);notifyAll();}public synchronized void hire(Class<? extends Robot> robotType, Assembler d) throws InterruptedException{for(Robot r : pool)if(r.getClass().equals(robotType)){pool.remove(r);r.assignAssembler(d);r.engage();// Power it up to do the taskreturn;}wait();// None availablehire(robotType, d);// Try again, recursively}public synchronized void release(Robot r){add(r);}}public class CarBuilder {public static void main(String[] args) throws InterruptedException {CarQueue chassisQueue = new CarQueue(),finishingQueue = new CarQueue();ExecutorService exec = Executors.newCachedThreadPool();RobotPool robotPool = new RobotPool();exec.execute(new EngineRobot(robotPool));exec.execute(new DriveTrainRobot(robotPool));exec.execute(new WheelRobot(robotPool));exec.execute(new Assembler(chassisQueue, finishingQueue, robotPool));exec.execute(new Reporter(finishingQueue));// Start everything running by producing chassis;exec.execute(new ChassisBuilder(chassisQueue));TimeUnit.SECONDS.sleep(7);exec.shutdownNow();}}?Car 是经由CarQueue从一个地方传送到另一个地方的，CarQueue是一种LinkedBlockingQueue类型。ChassisBuilder创建了一个未加修饰的Car， 并把它放到了一个CarQueue中。Assembler从一个CarQueue中取走Car, 并雇请Robot对其加工。CyclicBarrier使Assembler等待。直至所有的Robot都完成，并且在那一时刻它会将Car放置到将离开CarQueue中，然后被传送到下一个操作。最总的CarQueue的消费者是一个Report对象， 它只打印Car,以显示所有的任务都已经正确的完成了。Car将其所有方法都设置成了synchronized的。 正如它所表现出来的那样，在本例中，这是多余的， 因为在工程的内部， Car是通过队列一动的，并且在任何时， 只有一个任务能够在某辆车上工作。基本上，队列可以强制串行化地访问Car。但是这正是你可能会落入的陷阱--你可能会说“让我们尝试着通过不对Car类同步来进行优化， 因为看起来Car在这里并不需要同步。 但是当这个系统连接到另一个需要Car被同步的系统时，它就会崩溃。// 即Car可能会被多个线程使用，因此我们需要以明显的方式使其成为线程安全的