Where else to learn
wannacode is not the only place to learn Java, and it does not try to be. Here is where to go on when you want more.
SoftUni
Section titled "SoftUni"Software University (SoftUni) is a Bulgarian school for programmers: courses from the basics to a job, with exams, teachers and a large community. A good place if you want to learn in a group, on a schedule, with people who review your code.
The official documentation
Section titled "The official documentation"dev.java: Learn Java: the official tutorial by Oracle, from the first program to modern Java. When a lesson here gives you the idea, the documentation gives you every detail.