Being that I have to learn Java programming language in order to be able to make and understand evolutionary algorithms in Java, I’ve decided to search in Google looking for Java source code examples to start learning.
There are certainly plenty of hits (more than one and a half million of them!) If I had to select some first-cut starting point to explore Java source code, I’d choose Java Examples Organised by topic website (which also features examples of other popular and interesting languages like C/C++ or C#) Another good starting point is The Java Developers Almanac 1.4, which has, in my opinion, several very pedagogic examples.
A good free online electronic book, from Bruce Eckel, is Thinking in Java, 3rd Edition. All source code from examples developed in the book is available for downloading. There is a fourth edition of the book but it is only available for purchase. The author has other books on programming in other programming languages (e.g. C/C++) which could be interesting.