I have an idea, but I have no idea how to do it.

[Duck]

jMonkeyEngine is probably the best choice for Java. LWJGL is popular too, and Minecraft uses it.

If it's your first time programming in a language other than Lua, you might want to try Processing - it's a simpler version of Java with 2D and 3D graphics features. Or you can just use it as a graphics library for Java, because their code editor is kind of hard to use.

There are a lot more choices for C++. Many graphics engines don't include physics, but you should be able to integrate Bullet.

I don't have any experience with C++ engines, but these are the ones I've heard the most about:

• Crystal Space
  
• Ogre
  
• SDL (low-level, but easier than using OpenGL directly)
  

Isn't Ogre a rendering engine?