The main problem with Java for games is that you have to do graphics through a wrapper written in another language (AFAIK Minecraft uses LWJGL's OpenGL wrapper)

The main problem with Java for games is that you have to do graphics through a wrapper written in another language (AFAIK Minecraft uses LWJGL's OpenGL wrapper) and working from a language like Java, you lose some fine control of memory management. On the upside, it allows him to do rapid development, and you can even try Minecraft in the browser.