Primitive Data Types in Java

Java's primitive data types are very similar to those of C. The boolean type has been added. However the implementation of the data types has been substantially cleaned up in several ways.

1. Where C and C++ leave a number of issues to be machine and compiler dependent (for instance the size of an int) Java specifies everything.

2. Java prevents casting between arbitrary variables. Only casts between numeric variables and between sub and superclasses of the same object are allowed.

3. All numeric variables in Java are signed.

Here are the detailed data types:

boolean

1-bit. May take on the values true and false only.

true and false are defined constants of the language and are not the same as True and False, TRUE and FALSE, zero and nonzero, 1 and 0 or any other numeric value. Booleans may not be cast into any other type of variable nor may any other variable be cast into a boolean.

byte

1 signed byte (two's complement). Covers values from -128 to 127.

short

2 bytes, signed (two's complement), -32,768 to 32,767

int

4 bytes, signed (two's complement). -2,147,483,648 to 2,147,483,647. Like all numeric types ints may be cast into other numeric types (byte, short, long, float, double). When lossy casts are done (e.g. int to byte) the conversion is done modulo the length of the smaller type.

long

8 bytes signed (two's complement). Ranges from -9,223,372,036,854,775,808 to +9,223,372,036,854,775,807.

float

4 bytes, IEEE 754. Covers a range from 1.40129846432481707e-45 to 3.40282346638528860e+38 (positive or negative).

Like all numeric types floats may be cast into other numeric types (byte, short, long, int, double). When lossy casts to integer types are done (e.g. float to short) the fractional part is truncated and the conversion is done modulo the length of the smaller type.

double

8 bytes IEEE 754. Covers a range from 4.94065645841246544e-324d to 1.79769313486231570e+308d (positive or negative).

char

2 bytes, unsigned, Unicode, 0 to 65,535

Chars are not the same as bytes, ints, shorts or Strings.

sizeof isn't necessary in Java because all sizes are precisely defined. i.e. an int is always 4 bytes. This may not seem to be adequate when dealing with objects that aren't base data types. However even if you did know the size of a particular object, you couldn't do anything with it anyway. You cannot convert an arbitrary object into bytes and back again.