Java For Dummies Quick Reference

Data Types

The term data type refers to the type of data that can be stored in a variable. Sometimes, Java is called a “strongly typed language” because when you declare a variable, you must specify the variable’s type. Then the compiler ensures that you don’t try to assign data of the wrong type to the variable. The following example code generates a compiler error:

int x;

x = 3.1415;

Because x is declared as a variable of type int (which holds whole numbers), you can’t assign the value 3.1415 to it.

Java distinguishes between two kinds of data types: primitive types and reference types. Primitive types are the data types defined by the language itself. By contrast, reference types are types defined by classes in the Java application programming interface (API) or by classes you create rather than by the language itself.

Java defines eight primitive types:

Type	Explanation
int	A 32-bit (4-byte) integer value
short	A 16-bit (2-byte) integer value
long	A 64-bit (8-byte) integer value
byte	An 8-bit (1-byte) integer value
float	A 32-bit (4-byte) floating-point value
double	A 64-bit (8-byte) floating-point value
char	A 16-bit character using the Unicode encoding scheme
boolean	A true or false value

These primitive data types are discussed in their respective sections.