Hello,
please use the code tags, when you post code
see here How to type code blocks
For your issue, you need to use physics so that you have physical interaction between the objects of your scene
see
http://wiki.jmonkeyengine.org/doku.php/jme3:beginner:hello_physics?s[]=physics
http://wiki.jmonkeyengine.org/doku.php/jme3:beginner:hello_collision?s[]=physics
http://wiki.jmonkeyengine.org/doku.php/jme3:advanced:physics?s[]=physics
http://wiki.jmonkeyengine.org/doku.php/jme3:advanced:physics_listeners?s[]=physics