交通信号在Java中的多线程实现

可以通过使用线程和锁机制来实现。下面是一个简单的示例：

import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;

public class TrafficSignal {
    private final Lock lock = new ReentrantLock();
    private final Condition greenLight = lock.newCondition();
    private final Condition yellowLight = lock.newCondition();
    private final Condition redLight = lock.newCondition();
    private Signal currentSignal = Signal.GREEN;

    public void changeToGreen() {
        lock.lock();
        try {
            while (currentSignal != Signal.YELLOW) {
                greenLight.await();
            }
            currentSignal = Signal.GREEN;
            System.out.println("Green light is on.");
            yellowLight.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public void changeToYellow() {
        lock.lock();
        try {
            while (currentSignal != Signal.RED) {
                yellowLight.await();
            }
            currentSignal = Signal.YELLOW;
            System.out.println("Yellow light is on.");
            redLight.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    public void changeToRed() {
        lock.lock();
        try {
            while (currentSignal != Signal.GREEN) {
                redLight.await();
            }
            currentSignal = Signal.RED;
            System.out.println("Red light is on.");
            greenLight.signal();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }

    private enum Signal {
        GREEN,
        YELLOW,
        RED
    }
}

在上述示例中，TrafficSignal类使用了ReentrantLock和Condition来实现多线程控制。通过lock和unlock方法来获取和释放锁，使用await和signal方法来实现线程的等待和唤醒。

使用示例：

public class Main {
    public static void main(String[] args) {
        TrafficSignal trafficSignal = new TrafficSignal();

        Thread greenThread = new Thread(() -> {
            while (true) {
                trafficSignal.changeToGreen();
                try {
                    Thread.sleep(5000); // 绿灯持续5秒
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        Thread yellowThread = new Thread(() -> {
            while (true) {
                trafficSignal.changeToYellow();
                try {
                    Thread.sleep(2000); // 黄灯持续2秒
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        Thread redThread = new Thread(() -> {
            while (true) {
                trafficSignal.changeToRed();
                try {
                    Thread.sleep(3000); // 红灯持续3秒
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });

        greenThread.start();
        yellowThread.start();
        redThread.start();
    }
}

在上述示例中，创建了三个线程分别控制交通信号的绿灯、黄灯和红灯。每个线程通过调用TrafficSignal类中的相应方法来改变交通信号的状态，并且设置了不同的持续时间。

这个多线程实现可以用于模拟交通信号灯的运行，可以根据实际需求进行扩展和优化。

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