[使用备用线程交替打印]

Question

我正在努力实现这个： First Thread打印1，Second Thread打印2，Third Thread打印3，First Thread打印4，依此类推：

我做了这个并且正在努力：

    class Display implements Runnable
    {
        int threadId;
        static int v=1;
        static int turn=1;//init
        static Object monitor=new Object();
        Display(int id)
        {
            this.threadId=id;   
        }
        public void run() {// TODO Auto-generated method stub
            print();
        }
        private void print() {
            // TODO Auto-generated method stub
            while(v<100)
            {
                try {
                    Thread.sleep(1000);
                } catch (InterruptedException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }
            synchronized(monitor)
            {
                if(threadId==1)
                {
                   if(turn!=1)
                   {
                      try {
                        monitor.wait();
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                   }
                   else
                   {
                       System.out.println(threadId + ":"+v);
                       v++;
                       turn=2;
                       monitor.notifyAll();
                   }
                }
                else if(threadId==2)
                {
                    if(turn!=2)
                       {
                          try { 
                            monitor.wait();
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                       }
                       else
                       {
                           System.out.println(threadId+":"+v);   
                           v++;
                           turn=3;
                           monitor.notifyAll();
                       }
                }
                else
                {
                    if(turn!=3)
                       {
                          try {
                            monitor.wait();
                        } catch (InterruptedException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                        }
                       }
                       else
                       {
                           System.out.println(threadId+":"+v); 
                           v++;
                           turn=1;
                           monitor.notifyAll();
                       }    

                }
            }
            }
        }
    }

    public class Print {

        public static void main(String[] ar)
        {       
        Thread t1= new Thread(new Display(1));
        Thread t2= new Thread(new Display(2));
        Thread t3= new Thread(new Display(3));
        t1.start();
        t2.start();
        t3.start();
        }
    }

输出是这样的：

1:1
2:2
3:3
1:4
2:5

它达到了目的但是如果我还有两个可以交替打印的线程，那么我必须使用更多的If条件。

任何人都可以建议以更好的形式编写此代码，以更干净的方式完成该任务，以便在添加更多线程时可以扩展。

Answer 1

您需要为线程提供最高ID。在此之后，您可以使用模运算符简化代码。

class Display implements Runnable {
    int threadId;
    static int v = 1;
    static int higehstId = 0;
    static Object monitor = new Object();

    Display(int id) {
        this.threadId = id;
    }

    public void run() {
        print();
    }

    private void print() {
        while (v < 100) {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e1) {
                e1.printStackTrace();
            }
            synchronized (monitor) {
                if ((v - 1) % higehstId == threadId - 1) {
                    System.out.println(threadId + ":" + v);
                    v++;
                    monitor.notifyAll();
                } else {
                    try {
                        monitor.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
    }


    public static void main(String[] ar) {
        Thread t1 = new Thread(new Display(1));
        Thread t2 = new Thread(new Display(2));
        Thread t3 = new Thread(new Display(3));
        Thread t4 = new Thread(new Display(4));
        Thread t5 = new Thread(new Display(5));
        Display.higehstId = 5;
        t1.start();
        t2.start();
        t3.start();
        t4.start();
        t5.start();
    }
}

如果将v初始化为0并开始从0开始编号，则可以将if语句简化为：

if(v % highestId == threadId)