Classes and Objects:

Classes and Objects:

•The class is the unit of programming

•A Java program is a collection of classes

•Each class definition (usually) in its own .java file

•The file name must match the class name

•A class describes objects (instances)

•Describes their common characteristics: is a blueprint

•Thus all the instances have these same characteristics

•These characteristics are:

•Data fields for each object

•Methods (operations) that do work on the objects

Grouping Classes: The Java API,

•API = Application Programming Interface

•Java = small core + extensive collection of packages

•A package consists of some related Java classes:

•Swing: a GUI (graphical user interface) package

•AWT: Application Window Toolkit (more GUI)

•util: utility data structures (important to CS 187!)

•The import statement tells the compiler to make available classes and methods of another package

•A main method indicates where to begin executing a class (if it is designed to be run as a program)