Java Data Types — Java interactive lesson

As explained in the previous chapter, a variable in Java must be a specified data type:

int myNum = 5; // Integer (whole number)
float myFloatNum = 5.99f; // Floating point number
char myLetter = 'D'; // Character
boolean myBool = true; // Boolean
String myText = "Hello"; // String

Data types are divided into two groups:

Primitive data types - includes byte , short , int , long , float , double , boolean and char
Non-primitive data types - such as String , Arrays and Classes (you will learn more about these in a later chapter)

Primitive Data Types

A primitive data type specifies the type of a variable and the kind of values it can hold.

There are eight primitive data types in Java:

Data Type	Description
byte	Stores whole numbers from -128 to 127
short	Stores whole numbers from -32,768 to 32,767
int	Stores whole numbers from -2,147,483,648 to 2,147,483,647
long	Stores whole numbers from -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807
float	Stores fractional numbers. Sufficient for storing 6 to 7 decimal digits
double	Stores fractional numbers. Sufficient for storing 15 to 16 decimal digits
boolean	Stores true or false values
char	Stores a single character/letter or ASCII values

You Cannot Change the Type

Once a variable is declared with a type, it cannot change to another type later in the program:

int myNum = 5; // myNum is an int
// myNum = "Hello"; // Error: cannot assign a String to an int
String myText = "Hi"; // myText is a String
// myText = 123; // Error: cannot assign a number to a String

Note

This rule makes Java safer, because the compiler will stop you if you try to mix up types by mistake.

If you really need to change between types, you must use type casting or conversion methods (for example, turning an int into a double ).