Thank you both. I really appreciate your replies.
I think I can understand some parts of the input code. And as I learn more later, I will understand it better and maybe code my own. Thanks for that.
I cannot find the book, because I am not a native speaker and I don't live where it is sold
Today, I took a look at the Oracle's Java tutorials. And I think I can combine it with my present references and maybe find one or two more. I should take notes and I feel like it will be just okay. The rest is up to my ability to think algorithms and understand. And of course, to my creativity.
About the GUI, I decided to hold off for a while. After I master the most things about classes, methods and inheritance and packages etc., then I would take little steps into it. Coming from Basic (Not mastered everything of it - It was a 'very free time' hobby), that class thing is a little tough for me. I thought if I would ever give up, the reason would be classes. But Oracle tutorials cover the basics, and as I mentioned before, the rest is up to me.
To sum up, thank you. Both of you.