需求

编写一个程序，开启 3 个线程，这三个线程的 ID 分别为A、B、C，每个线程将自己的 ID 在屏幕上打印 10 遍，要求输出的结果必须按顺序显示。
如：ABCABCABC…… 依次递归。

测试代码

package juc.swap;

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

public class ThreadSwap {
    public static void main(String[] args) {
        Alternate alternate = new Alternate();
        AThread aThread = new AThread(alternate);
        BThread bThread = new BThread(alternate);
        CThread cThread = new CThread(alternate);

        new Thread(aThread).start();
        new Thread(bThread).start();
        new Thread(cThread).start();
    }

}

/* * 通过序号number来控制打印顺序 */
// 打印程序
class Alternate {

    private volatile int number = 1;

    Lock lock = new ReentrantLock();
    Condition condition = lock.newCondition();

    public void printA() {
        lock.lock();
        try {
            // while：保证被唤醒之后number是等于1的（解决虚假唤醒）
            while(number != 1) {
                condition.await();
            }
            System.out.println("A" + ":" + number);
            // 改变number的值，等待B被打印
            number = 2;
            condition.signalAll();
        } catch (InterruptedException e) {
        } finally {
            lock.unlock();
        }
    }

    public void printB() {
        lock.lock();
        try {
            while(number != 2) {
                condition.await();
            }
            System.out.println("B" + ":" + number);
            number = 3;
            condition.signalAll();
        } catch (InterruptedException e) {
        } finally {
            lock.unlock();
        }
    }

    public void printC() {
        lock.lock();
        try {
            while(number != 3) {
                condition.await();
            }
            System.out.println("C" + ":" + number);
            number = 1;
            condition.signalAll();
        } catch (InterruptedException e) {
        } finally {
            lock.unlock();
        }
    }
}

class AThread implements Runnable {
    private Alternate alternate;

    public AThread(Alternate alternate) {
        this.alternate = alternate;
    }

    @Override
    public void run() {
        for(int i = 0; i < 10; ++i) {
            alternate.printA();
        }
    }

}

class BThread implements Runnable {
    private Alternate alternate;

    public BThread(Alternate alternate) {
        this.alternate = alternate;
    }

    @Override
    public void run() {
        for(int i = 0; i < 10; ++i) {
            alternate.printB();
        }
    }
}

class CThread implements Runnable {
    private Alternate alternate;

    public CThread(Alternate alternate) {
        this.alternate = alternate;
    }

    @Override
    public void run() {
        for(int i = 0; i < 10; ++i) {
            alternate.printC();
        }
    }

}

其它

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