交替输出

题目：线程 1 输出 a 5 次，线程 2 输出 b 5 次，线程 3 输出 c 5 次。现在要求输出 abcabcabcabcabc

wait notify 版

public class SyncWaitNotify {
    private volatile int flag;
    private volatile int loopNumber;

    public SyncWaitNotify(int flag,int loopNumber){
        this.flag = flag;
        this.loopNumber = loopNumber;
    }

    public void print(int flag,int next,String str){
        for(int i=0;i<loopNumber;i++){
            synchronized (this){
                while (this.flag != flag){
                    try {
                        this.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
                System.out.print(str);
                this.flag = next;
                this.notifyAll();
            }
        }
    }

    public static void main(String[] args) {
        SyncWaitNotify syncWaitNotify = new SyncWaitNotify(1,5);
        new Thread(() -> {
            syncWaitNotify.print(1,2,"a");
        }).start();

        new Thread(() -> {
            syncWaitNotify.print(2,3,"b");
        }).start();

        new Thread(() -> {
            syncWaitNotify.print(3,1,"c");
        }).start();


    }
}

Lock 条件变量版

public class AwaitSignal extends ReentrantLock {
    private volatile int loopNumber;

    public AwaitSignal(int loopNumber) {
        this.loopNumber = loopNumber;
    }
    public void print(Condition condition,Condition next,String str){
        for(int i=0;i<loopNumber;i++){
            this.lock();
            try {
                try {
                    condition.await();
                    System.out.print(str);
                    next.signal();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            } finally {
                this.unlock();
            }
        }
    }

    public void start(Condition condition){
        this.lock();
        try {
            condition.signal();
        } finally {
            this.unlock();
        }

    }

    public static void main(String[] args) {
        AwaitSignal awaitSignal = new AwaitSignal(5);
        Condition aWait = awaitSignal.newCondition();
        Condition bWait = awaitSignal.newCondition();
        Condition cWait = awaitSignal.newCondition();

        new Thread(() -> {
            awaitSignal.print(aWait,bWait,"a");
        }).start();

        new Thread(() -> {
            awaitSignal.print(bWait,cWait,"b");
        }).start();

        new Thread(() -> {
            awaitSignal.print(cWait,aWait,"c");
        }).start();

        awaitSignal.start(aWait);
    }
}

Park Unpark 版

public class SyncPark {
    private int loopNumber;

    public Thread[] threads;

    public SyncPark(int loopNumber){
        this.loopNumber = loopNumber;
    }

    public void print(int next,String str){
        for(int i=0;i<loopNumber;i++){
            LockSupport.park();
            System.out.print(str);
            LockSupport.unpark(threads[next]);
        }
    }

    public void start(Thread thread){
        LockSupport.unpark(thread);
    }

    public static void main(String[] args) {
        SyncPark syncPark = new SyncPark(5);

        Thread t1 = new Thread(() -> {
            syncPark.print(1, "a");
        }, "t1");

        Thread t2 = new Thread(() -> {
            syncPark.print(2, "b");
        }, "t2");

        Thread t3 = new Thread(() -> {
            syncPark.print(0, "c");
        }, "t3");
        syncPark.threads = new Thread[]{t1,t2,t3};

        t1.start();
        t2.start();
        t3.start();
        syncPark.start(t1);
    }
}