Question

我在一本书中做了一个例子，它有一个线程示例，其中模拟了交通信号灯。我理解大部分程序，但是，我对这本书中“单独的线程将运行每个红绿灯”的部分感到困惑，似乎在主应用程序中只创建了一个线程？我有一个枚举，列出了我的红绿灯的所有常量。

public class TrafficLightSimulator implements Runnable {
private Thread thread;//holds the thread that runs the simulation
private TrafficLightColor color;//holds the traffic light color
boolean stop=false;//set to true to stop the simulation 
boolean changed=false;//true when the light has changed
public TrafficLightSimulator(TrafficLightColor inital){
color=inital;
thread=new Thread(this);
thread.start();
}
public TrafficLightSimulator(){
color=TrafficLightColor.RED;
thread=new Thread(this);
thread.start();
}
@Override
public void run() {
    //start up the light
    while(!stop){
        try{
            switch(color){
            case GREEN:
                Thread.sleep(10000);//green sleeps for 10 seconds
                break;
            case RED:
                Thread.sleep(2000);//yellow for 2 seconds
                break;
            case YELLOW:
                Thread.sleep(12000);//red for 12 seconds
                break;

            }
        }catch(Exception e){

        }
        changeColor();
    }
}
synchronized void changeColor(){
    switch(color){
    case RED:
        color=TrafficLightColor.GREEN;
        break;
    case YELLOW:    
        color=TrafficLightColor.RED;
        break;
    case GREEN:
        color=TrafficLightColor.YELLOW;     
    }
    changed=true;
    System.out.println("Notfiy Called We changed the light");
    notify();
}
synchronized void waitForChange(){
    try{
        while(!changed){
            System.out.println("waiting for Light to change");
            wait();
        }
        changed=false;

    }catch(Exception e){

    }
}
synchronized TrafficLightColor getColor(){
    return color;
}
synchronized void cancel(){
    stop=true;
}

}
 class Demo{
public static void main(String[]args){
    TrafficLightSimulator t1=new     TrafficLightSimulator(TrafficLightColor.YELLOW);
    for(int i=0;i<9;i++){
        System.out.println(t1.getColor());
        t1.waitForChange();
    }
    t1.cancel();
}
}

这是该计划的其余部分。

arr.splice(0,arr.length)

Answer 1

在每个println命令中打印一个线程的名称，它会显示哪个线程正在执行代码的哪一部分，它可以帮助您了解正在进行的操作。
只是：

System.out.println(Thread.currentThread().getName() + "==>"
                    + "Notfiy Called We changed the light");

如果您运行该应用程序，您将获得：

Thread-0==> start up the light
main==>YELLOW
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>RED
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>GREEN
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>YELLOW
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>RED
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>GREEN
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>YELLOW
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>RED
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
main==>GREEN
main==>waiting for Light to change
Thread-0==>Notfiy Called We changed the light
Thread-0==>Notfiy Called We changed the light

每个java应用程序中始终有一个 main 线程 - 该线程由Java虚拟机创建，主线程执行应用程序代码（调用public static void main()方法）。登记/> 应用程序可以创建和启动其他线程 - 在您的代码中，它的名称是Thread-0，它在构造函数中创建并启动 - 这里：

public TrafficLightSimulator(TrafficLightColor inital) {
    color = inital;
    thread = new Thread(this);  // creates a new thread
    thread.start();             // starts the new thread
}

请复制，粘贴并运行此代码，每个Thread.currentThread().getName() + "==>"命令中都包含println：

public class TrafficLightSimulator implements Runnable {

    private Thread thread;// holds the thread that runs the simulation
    private TrafficLightColor color;// holds the traffic light color
    boolean stop = false;// set to true to stop the simulation
    boolean changed = false;// true when the light has changed

    public TrafficLightSimulator(TrafficLightColor inital) {
        color = inital;
        thread = new Thread(this);
        thread.start();
    }

    public TrafficLightSimulator() {
        color = TrafficLightColor.RED;
        thread = new Thread(this);
        thread.start();
    }

    @Override
    public void run() {
        // start up the light
        System.out.println(Thread.currentThread().getName() +"==>" +" start up the light" );
        while (!stop) {
            try {
                switch (color) {
                case GREEN:
                    Thread.sleep(10000);// green sleeps for 10 seconds
                    break;
                case RED:
                    Thread.sleep(2000);// yellow for 2 seconds
                    break;
                case YELLOW:
                    Thread.sleep(12000);// red for 12 seconds
                    break;

                }
            } catch (Exception e) {

            }
            changeColor();
        }
    }

    synchronized void changeColor() {
        switch (color) {
        case RED:
            color = TrafficLightColor.GREEN;
            break;
        case YELLOW:
            color = TrafficLightColor.RED;
            break;
        case GREEN:
            color = TrafficLightColor.YELLOW;
        }
        changed = true;
        System.out.println(Thread.currentThread().getName() + "==>" + "Notfiy Called We changed the light");
        notify();
    }

    synchronized void waitForChange() {
        try {
            while (!changed) {
                System.out.println(Thread.currentThread().getName() + "==>" +  "waiting for Light to change");
                wait();
            }
            changed = false;

        } catch (Exception e) {

        }
    }

    synchronized TrafficLightColor getColor() {
        return color;
    }

    synchronized void cancel() {
        stop = true;
    }

    public static void main(String[] args) {
        TrafficLightSimulator t1 = new TrafficLightSimulator(TrafficLightColor.YELLOW);
        for (int i = 0; i < 9; i++) {
            System.out.println(Thread.currentThread().getName() + "==>" + t1.getColor());
            t1.waitForChange();
        }
        t1.cancel();
    }

}

Threaded TrafficLightExample众多线程？

1 个答案: