经典面试题之线程按顺序交替打印

public class  {

  public static void main(String[] args) {
    AlternateDemo ad = new AlternateDemo();
    new Thread(new Runnable() {
      
      public void run() {
        for (int i = 1; i <= 20; i++) {
          ad.loopA(i);
        }
      }
    }, "A").start();

    new Thread(new Runnable() {
      
      public void run() {

        for (int i = 1; i <= 20; i++) {
          ad.loopB(i);
        }
      }
    }, "B").start();

    new Thread(new Runnable() {
      
      public void run() {

        for (int i = 1; i <= 20; i++) {
          ad.loopC(i);  
          System.out.println("-----------------------------------");
        }

      }
    }, "C").start();
  }

}

class AlternateDemo{

  private int number = 1; 

  private Lock lock = new ReentrantLock();
  private Condition condition1 = lock.newCondition();
  private Condition condition2 = lock.newCondition();
  private Condition condition3 = lock.newCondition();

  /**
    * @param totalLoop : 循环第几轮
  */
  public void loopA(int totalLoop){
    lock.lock();

    try {
      //1. 判断
      if(number != 1){
        condition1.await();
      }

      //2. 打印
      for (int i = 1; i <= 1; i++) {
        System.out.println(Thread.currentThread().getName() + "t" + i + "t" + totalLoop);
      }

      //3. 唤醒
      number = 2;
      condition2.signal();
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      lock.unlock();
    }
  }

  public void loopB(int totalLoop){
    lock.lock();

    try {
      //1. 判断
      if(number != 2){
        condition2.await();
      }

      //2. 打印
      for (int i = 1; i <= 1; i++) {
        System.out.println(Thread.currentThread().getName() + "t" + i + "t" + totalLoop);
      }

      //3. 唤醒
      number = 3;
      condition3.signal();
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      lock.unlock();
    }
  }

  public void loopC(int totalLoop){
    lock.lock();

    try {
      //1. 判断
      if(number != 3){
        condition3.await();
      }

      //2. 打印
      for (int i = 1; i <= 1; i++) {
        System.out.println(Thread.currentThread().getName() + "t" + i + "t" + totalLoop);
      }

      //3. 唤醒
      number = 1;
      condition1.signal();
    } catch (Exception e) {
      e.printStackTrace();
    } finally {
      lock.unlock();
    }
  }

}