Do you know a good guide for Java, such as "dive into python" for python?
If I searched google I expect I would find tons of random guides, but trying them all until I found a good one could take ages... that's why I am asking: do you already know one in particular? one you KNOW is good?
I already know C, PHP and a bit of Python, if that matters.
Deitel's Java: How to Program. When you're done with the book (and all its exercises), you will know most of what you'll ever need to know about Java.
The Java Tutorials are practical guides for programmers who want to use the Java programming language to create applications. They include hundreds of complete, working examples, and dozens of lessons. Groups of related lessons are organized into "trails".
When I need to learn something about Java, the link I provided you is where I go. This has proved to be a really valuable source of information about Java to me.
Just to start:
If you already know some other languages and you're mostly interested in learning how to write good Java code, I would recommend Effective Java by Joshua Bloch. If you want to learn the basics of the language, The Java Tutorials that Leniel mentioned are good.
Bruce Eckel's Thinking in Java has the advantage of being free (e-book).
I find books from the Head First series really great so my recommendation would be:
I would suggest Java Passion site, it is really very good and helpful.