Enthuware

My study book say that DataInputStream is not in the exam. Is this true? Finding it hard to know what to learn when your exams come up with questions on material thats not supposed to be on the exam according to my book.

We have received feedback from our customers that they got question on this class. That is why we have included it in our question bank.
Can't really comment on the book. Most books are static. Once they are published, authors rarely make any changes other than fixing errors. So you might want to check with the author of your book about it.

It's in the Serialisation Chapter (Appendix) of K&B 7:

... It turns out that while the exam was being created, it was decided that those two classes wouldn't be on the exam after all, but someone forgot to remove them from the objectives! So you get a break. ...

But it obviously doesn't hurt to know about these two classes

Removing from the objectives is the easy part. We have seen them modifying the objectives for correcting errors. So if they wanted, they could have easily removed this topic from the objectives.
However, some candidates have reported getting question on it.

Note there is readChar() and writeChar() methods! But not readChars()!