Who this book is for
This book is aimed at developers who are already familiar with object-oriented programming principles, know the basics of game development, and want to use the power of Libgdx to make awesome cross-platform games without the hassle of having to deal with platform-specific nonsense.
Although Libgdx is based on Java, having experience with the language is only recommended and not a must. It can easily be learned as you go, even more so when coming from C++ or C#.