Foo.java

class Foo {
    private Object lock;
    private boolean oneDone;
    private boolean twoDone;

    public Foo() {
        lock = new Object();
        oneDone = false;
        twoDone = false;
    }

    public void first(Runnable printFirst) throws InterruptedException {

        // printFirst.run() outputs "first". Do not change or remove this line.
        synchronized (lock){
            printFirst.run();
            oneDone = true;
            lock.notifyAll();
        }

    }

    public void second(Runnable printSecond) throws InterruptedException {

        // printSecond.run() outputs "second". Do not change or remove this line.
        synchronized(lock){
            while(!oneDone){
                lock.wait();
            }
            printSecond.run();
            twoDone = true;
            lock.notifyAll();


        }
    }

    public void third(Runnable printThird) throws InterruptedException {

        // printThird.run() outputs "third". Do not change or remove this line.
        synchronized(lock){
            while(!twoDone){
                lock.wait();
            }
            printThird.run();

        }
        
    }
}