Java-交替打印偶数和奇数

常见的一道面试题，认真想一想，自己写出来还是对wait()和notify()的理解有好处的，但是还是推荐使用reentrantlock去实现，更灵活吧。

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package com.ilovewl.interview.concurrent;

/**
 * 主要就是两个线程占用同一把锁，一个标志位保存当前应该输出偶数还是奇数
 * @author liuchangrong
 */
public class PrintNumber {

  private static final int MAX_NUMBER = 10;

  public static void main(String[] args) {
    Counter lock = new Counter();
    new Thread(new A(lock)).start();
    new Thread(new B(lock)).start();
  }

  //输出偶数
  static class A implements Runnable {
    int init = 0;
    boolean flag = true;
    private Counter lock;

    public A(Counter lock) {
      this.lock = lock;
    }

    @Override
    public void run() {
      while (init <= MAX_NUMBER) {
        synchronized (lock) {
          if(!lock.odd) {
            try {
              lock.wait();
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
          System.out.println(init);
          try {
            Thread.sleep(1000);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          init = init + 2;
          //通知另外一个进程
          lock.notifyAll();
          //改变下一个状态
          lock.odd = !lock.odd;
        }
      }
    }
  }

  //输出奇数
  static class B implements Runnable {
    int init = 1;
    private Counter lock;

    public B(Counter lock) {
      this.lock = lock;
    }

    @Override
    public void run() {
      while (init <= MAX_NUMBER ) {
        synchronized (lock) {
          if(lock.odd) {
            try {
              lock.wait();
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
          System.out.println(init);
          try {
            Thread.sleep(1000);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          init = init + 2;
          lock.notifyAll();
          lock.odd = !lock.odd;
        }
      }
    }
  }
  static class Counter{
    //初始值为true,表示输出偶数，奇数的线程就等待
    //如果为false,表示输出奇数，偶数的线程就等待
    public boolean odd = true;
  }
}

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使用ReentrantLock实现：

package com.ilovewl.interview.concurrent;

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

/**
 * 使用ReentrantLock打印奇数和偶数
 * @author liuchangrong
 */
public class PrintNumber2 {
  private static final int MAX_NUMBER = 10;
  static Counter lock = new Counter();
  static Condition a = lock.newCondition();
  static Condition b = lock.newCondition();
  public static void main(String[] args) {
    new Thread(new A(lock)).start();
    new Thread(new B(lock)).start();
  }

  //输出偶数
  static class A implements Runnable {
    int init = 0;
    private Counter lock;

    public A(Counter lock) {
      this.lock = lock;
    }

    @Override
    public void run() {
      while (init <= MAX_NUMBER) {
        lock.lock();
        try {
          if (!lock.odd) {
            try {
              a.await();
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
          System.out.println(init);
          try {
            Thread.sleep(1000);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          init = init + 2;
          b.signal();
          lock.odd = !lock.odd;
        } finally {
          lock.unlock();
        }
      }
    }
  }

  //输出奇数
  static class B implements Runnable {
    int init = 1;
    private Counter lock;

    public B(Counter lock) {
      this.lock = lock;
    }

    @Override
    public void run() {
      while (init <= MAX_NUMBER ) {
        lock.lock();
        try {
          if (lock.odd) {
            try {
              b.await();
            } catch (InterruptedException e) {
              e.printStackTrace();
            }
          }
          System.out.println(init);
          try {
            Thread.sleep(1000);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
          init = init + 2;
          a.signal();
          lock.odd = !lock.odd;
        }finally {
          lock.unlock();
        }
      }
    }
  }
  static class Counter extends ReentrantLock {
    //初始值为true,表示先输出偶数，奇数的线程就等待
    public boolean odd = true;
    public Counter(){
      super(true);
    }
  }
}

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如果有什么问题的话，欢迎留言讨论！