Introduction to OOP

Chapter 4: Classes and Methods:

Visibility Modifiers

The terms public and private are used to differentiate the internal and external aspects of a class.

public features can be seen and manipulated by anybody -- they are the external (interface or service) view.
private features can be manipuated only within a class. They are the internal (implementation) view.

Typically methods are public and data fields are private, but either can be placed in either category.