1114. 按序打印

代码：

import java.util.concurrent.atomic.AtomicInteger;

class Foo {
    private final AtomicInteger atomic = new AtomicInteger(0);

    public Foo() {

    }

    public void first(Runnable printFirst) throws InterruptedException {

        // printFirst.run() outputs "first". Do not change or remove this line.
        printFirst.run();
        //+1
        atomic.incrementAndGet();
    }

    public void second(Runnable printSecond) throws InterruptedException {
        //没执行过first则一直不跑second
        while (atomic.get() != 1) {
        }
        // printSecond.run() outputs "second". Do not change or remove this line.
        printSecond.run();
        //+1
        atomic.incrementAndGet();
    }

    public void third(Runnable printThird) throws InterruptedException {
        while (atomic.get() != 2) {
        }
        // printThird.run() outputs "third". Do not change or remove this line.
        printThird.run();
    }
}