java双线程交替打印1-100的数字

第一版代码

Thread threadOdd = new Thread(() -> {
for (int i = 1; i <= 99; i+=2){
        synchronized (sharedThing){
            System.out.println(Thread.currentThread().getName() + " " + i);
            try {
                sharedThing.wait();
                sharedThing.notify();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    }
});

Thread threadEven = new Thread(() -> {
for (int i = 2; i <= 100; i += 2) {
    synchronized (sharedThing) {
        System.out.println(Thread.currentThread().getName() + " " + i);
        sharedThing.notify();
        try {
            sharedThing.wait();
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
}
});

threadOdd.start();
Thread.sleep(1000);
threadEven.start();`

效果看起来还可以，但是稍微改动一下threadOdd就会出现问题，比如这样：

Thread threadOdd = new Thread(() -> {
for (int i = 1; i <= 99; i+=2){
        synchronized (sharedThing){
            System.out.println(Thread.currentThread().getName() + " " + i);
            try {
                sharedThing.wait();
                sharedThing.notify();
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
        try {
            Thread.sleep(10000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
    }
});

结果为：

threadOdd抢占共享资源的过程被延长了，导致threadEven先占用了资源，threadOdd无法被唤醒，死锁了

所以修改一下，加入奇数偶数校验，保证打印奇数线程只打印奇数，偶数线程只打印偶数

让两个线程严格按照顺序执行

第二版代码

    Thread threadOdd = new Thread(() -> {
        while (cur < 100){
            synchronized (sharedThing){
                if(cur % 2 == 1){
                    System.out.println(Thread.currentThread().getName() + ":" + cur);
                    cur += 1;
                    try {
                        sharedThing.wait();
                        sharedThing.notify();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
            try {
                Thread.sleep(10000);
            } catch (InterruptedException e) {
                throw new RuntimeException(e);
            }
        }
    });

    Thread threadEven = new Thread(() -> {
        while (cur < 100){
            synchronized (sharedThing){
                if(cur % 2 == 0){
                    sharedThing.notify();
                    System.out.println(Thread.currentThread().getName() + ":" + cur);
                    cur += 1;
                    try {
                        sharedThing.wait();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        }
    });

    threadOdd.start();
    threadEven.start();
}

效果如下

使用ReentrantLock和Condition的代码

奇数线程准备奇数数字1,3,5，... ,49

偶数线程准备偶数数字2,4,6, ... ,50

condition负责保证奇数偶数打印的顺序

public static void reenTrantLockPrint(){
        ReentrantLock reentrantLock = new ReentrantLock();
        Condition oddCondition = reentrantLock.newCondition();
        Condition evenCondition = reentrantLock.newCondition();
        new Thread(() -> {
            int i = 1;
            while(i <= 50){
                reentrantLock.lock();
                if(i % 2 == 1){
                    System.out.println(Thread.currentThread().getName() + " 打印" + i);
                    evenCondition.signal();
                    i+=2;
                    try {
                        oddCondition.await();
                        reentrantLock.unlock();
                    } catch (InterruptedException e) {
                        throw new RuntimeException(e);
                    }
                }
            }
        },"odd").start();

        new Thread(() -> {
            int i = 2;
            while(i <= 50){
                reentrantLock.lock();
                System.out.println(Thread.currentThread().getName() + " 打印" + i);
                oddCondition.signal();
                i+=2;
                try {
                    evenCondition.await();
                    reentrantLock.unlock();
                } catch (InterruptedException e) {
                    throw new RuntimeException(e);
                }
            }
        },"even").start();
    }

效果

才疏学浅，如果有错误或不准确的地方，欢迎大家指出