I made an as-simple-as-possible 3D renderer in Java 1.0, so that my undergrad students could extend it and could learn how 3D rendering works. I've included all the source code for the applet.
In addition to 3D rendering and modeling, this simple car example shows several things: (i) how to implement sliders and buttons, (ii) how you can interactively vary shape dimensions, (iii) how to interact with color as both Red/Green/Blue (RGB) and Hue/Saturation/Value (HSV).
Instructions: Drag the mouse to change the camera view. Drag on the sliders to change dimensions and color. Note that if you vary RGB, then HSV will change, and if you vary HSV, then RGB will change.