Object-oriented design (OOD) uses objects to design programs. To use an object, you do not need to know the makeup of the object. This information might be hidden from you. However, you need to know the functions of the object (such as buttons) and how to use them. You can use an object by itself or with other objects, but you cannot modify the functions of the object. To create objects, you first need to learn to create classes; to know what type of classes to create, you need to know what an object stores and what operations are needed to manipulate an objects data.

The aim of OOD is to build software from software components called classes and to use the various methods provided by those classes. In OOD, you first identify the object, then identify the relevant data, and then identify operations needed to manipulate that data. One basic principle of OOD is encapsulation