Java Real Simple Solution
\nclass Foo {\n    private volatile int num = 1;\n    public Foo() {\n\n    }\n\n    public void first(Runnable printFirst) throws InterruptedException {\n     
```\nclass Foo {\n    private volatile int num = 1;\n    public Foo() {\n\n    }\n\n    public void first(Runnable printFirst) throws InterruptedException {\n        while(num != 1){\n        }\n\n        // printFirst.run() outputs "first". Do not change or remove this line.\n        printFirst.run();\n        num++;\n    }\n\n    public void second(Runnable printSecond) throws InterruptedException {\n        while(num != 2){\n        }\n        // printSecond.run() outputs "second". Do not change or remove this line.\n        printSecond.run();\n        num++;\n    }\n\n    public void third(Runnable printThird) throws InterruptedException {\n        while(num != 3){\n        }\n        // printThird.run() outputs "third". Do not change or remove this line.\n        printThird.run();\n        num++;\n    }\n}\n```
['Java']