使用lock,condition实现三个线程循环打印ABC

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

public class TestABCAlternate {
    public static void main(String[] args) {
        AlterNate a = new AlterNate();

        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 20; i++) {
                    a.loopA(i);
                }
            }
        },"A").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 20; i++) {
                    a.loopB(i);
                }
            }
        },"B").start();

        new Thread(new Runnable() {
            @Override
            public void run() {
                for (int i = 1; i <= 20; i++) {
                    a.loopC(i);
                }
            }
        },"C").start();


    }

}

class AlterNate{
    private int number = 1;
    private Lock lock = new ReentrantLock();
    private Condition condition1 = lock.newCondition();
    private Condition condition2 = lock.newCondition();
    private Condition condition3 = lock.newCondition();

    public void loopA(int loopNum){
        lock.lock();
        try{
            // 判断
            if(number != 1){
                condition1.await();
            }

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

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

    public void loopB(int loopNum){
        lock.lock();
        try{
            if(number != 2){
                condition2.await();
            }

            for(int i=1;i<=1;i++){
                System.out.println(Thread.currentThread().getName()+" "+i+" "+loopNum);
            }

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

    public void loopC(int loopNum){
        lock.lock();
        try{
            if(number != 3){
                condition3.await();
            }

            for(int i=1;i<=1;i++){
                System.out.println(Thread.currentThread().getName()+" "+i+" "+loopNum);
            }

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

非静态方法的锁为this.  静态方法的锁为对应的Class实例.