java - 3个线程按顺序打印数字

Question

我正在尝试编写一个简单的代码来按顺序打印数字。场景就像

Thread  Number
T1        1
T2        2
T3        3
T1        4
T2        5
T3        6
T1        7
T2        8
T3        9
...and so on.

这里是

public class ThreadNumberPrinter {

    Object monitor = new Object();
    AtomicInteger number = new AtomicInteger(1);

    public static void main(String[] args) {
        ThreadNumberPrinter tnp = new ThreadNumberPrinter();
        Thread t1 = new Thread(tnp.new Printer(1, 3));
        Thread t2 = new Thread(tnp.new Printer(2, 3));
        Thread t3 = new Thread(tnp.new Printer(3, 3));

        t3.start();
        t1.start();
        t2.start();
    }

    class Printer implements Runnable {

        int threadId;
        int numOfThreads;

        public Printer(int id, int nubOfThreads) {
            threadId = id;
            this.numOfThreads = nubOfThreads;
        }

        public void run() {
            print();
        }

        private void print() {
            try {
                while (true) {
                    Thread.sleep(1000l);
                    synchronized (monitor) {
                        if (number.get() % numOfThreads != threadId) {
                            monitor.wait();
                        } else {
                            System.out.println("ThreadId [" + threadId
                                    + "] printing -->"
                                    + number.getAndIncrement());
                            monitor.notifyAll();
                        }
                    }
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }

       }

   }

但是就在第二个线程运行并打印数字 2 之后，所有线程都进入等待阶段并且什么也没有打印。我不确定我哪里做错了。任何帮助将不胜感激。

Answer 1

  public class TestClass {

    private volatile Integer count = 1;
    private volatile Integer threadIdToRun = 1;
    private Object object = new Object();

    public static void main(String[] args) {

        TestClass testClass = new TestClass();
        Thread t1 = new Thread(testClass.new Printer(1));
        Thread t2 = new Thread(testClass.new Printer(2));
        Thread t3 = new Thread(testClass.new Printer(3));

        t1.start();
        t2.start();
        t3.start();
    }

    class Printer implements Runnable {

        private int threadId;

        public Printer(int threadId) {
            super();
            this.threadId = threadId;
        }

        @Override
        public void run() {
            try {
                while (count <= 20) {
                    synchronized (object) {
                        if (threadId != threadIdToRun) {
                            object.wait();
                        } else {
                            System.out.println("Thread " + threadId + " printed " + count);
                            count += 1;

                            if (threadId == 1)
                                threadIdToRun = 2;
                            else if (threadId == 2)
                                threadIdToRun = 3;
                            else if (threadId == 3)
                                threadIdToRun = 1;

                            object.notifyAll();
                        }
                    }
                }
            } catch (Exception e) {
                e.printStackTrace();
            }

        }
    }
}

以上程序给出输出

Thread 1 printed 1
Thread 2 printed 2
Thread 3 printed 3
Thread 1 printed 4
Thread 2 printed 5
Thread 3 printed 6
Thread 1 printed 7
Thread 2 printed 8
Thread 3 printed 9
Thread 1 printed 10
Thread 2 printed 11
Thread 3 printed 12
Thread 1 printed 13
Thread 2 printed 14
Thread 3 printed 15
Thread 1 printed 16
Thread 2 printed 17
Thread 3 printed 18
Thread 1 printed 19
Thread 2 printed 20