The Primitive Types
Java defines eight primitive types of data: byte, short, int, long, char, float, double, and boolean. The primitive types are also commonly referred to as simple types, and both terms will be used in this book. These can be put in four groups:
Integers This group includes byte, short, int, and long, which are for whole-valued signed numbers.
Floating-point numbers This group includes float and double, which represent numbers with fractional precision.
Characters This group includes char, which represents symbols in a character set, like letters and numbers.
Boolean This group includes boolean, which is a special type for representing true/false values.
You can use these types as-is, or to construct arrays or your own class types. Thus, they form the basis for all other types of data that you can create.
The primitive types represent single values—not complex objects. Although Java is otherwise completely object-oriented, the primitive types are not. They are analogous to the simple types found in most other non–object-oriented languages. The reason for this is efficiency. Making the primitive types into objects would have degraded performance too much.
The primitive types are defined to have an explicit range and mathematical behavior. Languages such as C and C++ allow the size of an integer to vary based upon the dictates of the execution environment. However, Java is different. Because of Java’s portability requirement, all data types have a strictly defined range. For example, an int is always 32 bits, regardless of the particular platform. This allows programs to be written that are guaranteed to run without porting on any machine architecture. While strictly specifying the size of an integer may cause a small loss of performance in some environments, it is necessary in order to achieve portability.
Let’s look at each type of data in turn.