3个线程分别打印123

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

public class ThreadTest {

    public static void main(String[] args) {
        new Thread(new PrintNumber(1)).start();
        new Thread(new PrintNumber(2)).start();
        new Thread(new PrintNumber(3)).start();
    }
}

class PrintNumber implements Runnable {

    private static final ReentrantLock LOCK = new ReentrantLock();

    private static final Condition[] pArray = new Condition[3];

    private final Integer printNumber;

    private volatile static Integer incNumber = 1;

    static {
        //打印1的条件
        pArray[0] = LOCK.newCondition();
        //打印2的条件
        pArray[1] = LOCK.newCondition();
        //打印3的条件
        pArray[2] = LOCK.newCondition();
    }

    PrintNumber(Integer pn) {
        this.printNumber = pn;
    }

    void print() {
        LOCK.lock();
        try {
            //否决条件
            while (!incNumber.equals(printNumber)) {
                //挂起不符合条件的线程
                Integer temp = printNumber - 1;
                pArray[temp].await();
            }
            //action
            System.out.println(incNumber);
            incNumber++;
            if (incNumber > 3) {
                incNumber = 1;
            }
            //通知下个打印的线程 激活
            Integer temp = incNumber - 1;
            pArray[temp].signalAll();

        } catch (Exception ex) {
            ex.printStackTrace();
        } finally {
            LOCK.unlock();
        }
    }

    @Override
    public void run() {
        while (true) {
            print();
        }
    }
}

利用 ReentrantLock 的condition 合理的激活 对应的线程  杜绝 提前激活不需要的线程