Classes and Data Types

Programming is concerned with specifying how data of various kinds is to be processed, massaged, manipulated, or transformed. Since classes define the types of objects that a program will work with, you can consider defining a class to be the same as defining a data type. Thus, Hat is a type of data, as is Tree, and any other class you care to define. Java also contains a library of standard classes that provide you with a whole range of programming tools and facilities. For the most part then, your Java program will process, massage, manipulate, or transform class objects.

There are some basic types of data in Java that are not classes, and these are called primitive types. I will go into these in detail in the next chapter, but they are essentially data types for numeric values such as 99 or 3.75, for single characters such as A or ?, and for logical values that can be true or false. Java also has classes that correspond to each of the primitive data types for reasons that you will see later on, so there is an Integer class that defines objects that encapsulate integers, for example. Every entity in your Java program that is not of a primitive data type will be an object of a class - either a class that you define yourself, a class supplied as part of the Java environment, or a class that you obtain from somewhere else, such as from a specialized support package.