Question on Joint what is the First DOF Axis for

joint=new HingeJoint(hookNode.getControl(RigidBodyControl.class), // A

pendulumNode.getControl(RigidBodyControl.class), // B

new Vector3f(0f, 0f, 0f), // pivot point local to A

new Vector3f(0f, 1f, 0f), // pivot point local to B

Vector3f.UNIT_Z, // DoF Axis of A (Z axis) <

Vector3f.UNIT_Z ); // DoF Axis of B (Z axis)

Can anyone explain this to me in real world terms.
A hinge :on a door one side stays still
A wheel :one side stays still and the other rotates

Am I just confused or am I not thinking correctly?

Thanks for any help.