Summary and Overview

Reusing code.

Information hiding.

Enhancing performance.

Creating global variables.

Overriding system-level functions.

Variables to become constants.

A class to reuse properties and methods of another class.

Direct access to private members of another class.

One name to have multiple forms of implementation.

A single class to inherit from multiple parents.

Variables to change their types dynamically.

Direct manipulation of internal state.