LeetCode（多线程）- 1114. 按序打印

// 解决方案(1)
class Foo {
    public Foo() {
    }
    volatile int count=1;
    public void first(Runnable printFirst) throws InterruptedException {
        printFirst.run();
        count++;
    }
    public void second(Runnable printSecond) throws InterruptedException {
        while (count!=2);
        printSecond.run();
        count++;
    }
    public void third(Runnable printThird) throws InterruptedException {
        while (count!=3);
        printThird.run();
    }
}
// 解决方案(2)
class Foo {
    private boolean firstFinished;
    private boolean secondFinished;
    private Object lock = new Object();
    public Foo() {
    }
    public void first(Runnable printFirst) throws InterruptedException {
        synchronized (lock) {
            // printFirst.run() outputs "first". Do not change or remove this line.
            printFirst.run();
            firstFinished = true;
            lock.notifyAll(); 
        }
    }
    public void second(Runnable printSecond) throws InterruptedException {
        synchronized (lock) {
            while (!firstFinished) {
                lock.wait();
            }
            // printSecond.run() outputs "second". Do not change or remove this line.
            printSecond.run();
            secondFinished = true;
            lock.notifyAll();
        }
    }
    public void third(Runnable printThird) throws InterruptedException {
        synchronized (lock) {
           while (!secondFinished) {
                lock.wait();
            }
            // printThird.run() outputs "third". Do not change or remove this line.
            printThird.run();
        } 
    }
}