Java3D Collision Detecting

How to do Collision Detecting?
Hello i am new in this Forum.
Well i need an very simple example for collision detecting.
I searched for something like this for years.
I tried lots of times but could not find an answer.

Maybe you have a code for me, which should include:
-you can walk with the ArrowKeys (Forward, Backward, left, right)
-there are two colorcubes on different places, if you walk to them you cant walk through them,

I would be very pleased to your answer,
Regards,
the Developer_X
PS: please no links, cause i found lots of codes with the subject ‘ease or simple’ but they were to complicadet,
thanks for your answer
the Developer_X