This post is a brief tutorial on how to use display lists in OpenGL. An working and self-contained example is given below using LWJGL.
Display lists are an essential feature of OpenGL to improve the rendering performance of your application. You can think of them as kind of a macro for OpenGL commands that you name, record and call at some point in your game. More specifically, you assign an integer handle to a sequence of OpenGL commands and call the commands identified by that handle when you need them.

This blog post explains a common and versatile approach to OpenGL picking called “ray picking”. An example in pseudo-code is given below.

Picking is the process of finding objects in you scene based on user input. Most commonly, you want to determine what object a user has clicked with his mouse. In this case the 2D mouse coordinates serve as a reference on the view port to identify the projected objected that has been clicked. A similar scenario is a first person shooter, where the gun serves as the picking pointer, however in world space coordinates. If you shoot your gun, the trajectory of the bullet is traced through your scene and collisions are detected.