利用Condition来实现多线程交替打印ABC

使用重入锁 ReentrantLock先来获得,.newCondition对象，Condition 可以用来指定队列，唤醒指定队列中的线程，这样在多线程环境下会有更高的效率；

package morning;

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

//4.三个线程交替输出A B C ，输出20遍。
public class Lock_Condition_ABC {
    private static Lock lock = new ReentrantLock();
    private static Condition A = lock.newCondition();
    private static Condition B = lock.newCondition();
    private static Condition C = lock.newCondition();

    private static int count = 0;
    private  static int sum=1;

    static class ThreadA extends Thread {
        @Override
        public void run() {
            try {
                lock.lock();

                for (int i = 0; i < 10; i++) {
                    while (count % 3 != 0){//注意这里是不等于0，也就是说没轮到该线程执行，之前一直等待状态
                        A.await(); //该线程A将会释放lock锁，构造成节点加入等待队列并进入等待状态
                    }
                    System.out.println("-------第"+sum+"次--------");
                    System.out.println("A");
                    count++;
                    B.signal(); // A执行完唤醒B线程
                }

            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }

    static class ThreadB extends Thread {
        @Override
        public void run() {
            try {
                lock.lock();
                for (int i = 0; i < 10; i++) {
                    while (count % 3 != 1)
                        B.await();// B释放lock锁，当前面A线程执行后会通过B.signal()唤醒该线程
                    System.out.println("B");
                    count++;
                    C.signal();// B执行完唤醒C线程
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }

    static class ThreadC extends Thread {
        @Override
        public void run() {
            try {
                lock.lock();
                for (int i = 0; i < 10; i++) {
                    while (count % 3 != 2)
                        C.await();// C释放lock锁
                    System.out.println("C");
                    count++;
                    sum++;
                    A.signal();// C执行完唤醒A线程
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            } finally {
                lock.unlock();
            }
        }
    }

    public static void main(String[] args) throws InterruptedException {
        new ThreadA().start();
        new ThreadB().start();
        new ThreadC().start();
    }
}