“More recently, a new generation of languages has begun to emerge. These languages—Small-Talk, C++, Java—are object-oriented. They treat a data structure—for instance, a picture to be drawn on the screen—as an “object” with its own internal state, such as where it is to be drawn or what color it is. These objects can receive instructions from other objects. To understand why this is useful, imagine that you are writing a program for a video game involving bouncing balls. Each ball on the screen is defined as a different object. The program specifies rules of behavior that tell the object how to draw itself on the screen, move, bounce, and interact with other objects in the game. Each ball will exhibit similar behavior, but each will be in a slightly different state, because each will be in its own position on the screen and will have its own color, velocity, size, and so forth.”