It was when I first wrote the program.
Now, it is not.
It may seem strange that a correctly written program can become buggy without being altered. But this is actually common. Circumstances external to a program often change, so the program must be revised. Much of what professional programmers do is program maintainance: keeping programs up to date with changing requirements.
You have reached the end of the chapter. If you are unclear about it, take a break, and then read the chapter again. Or find a friend that knows how to do this, perhaps the same friend you annoyed at the end of the previous chapter. This stuff is much easier if you see someone do it a few times.
You may wish to review the following. Click on a subject that interests you to go to where it was discussed.
The next chapter will discuss the beginning elements of the Java language (at last!).
You have reached the end of the chapter.