There are 8 primitive data types. All other variable types are objects that are created in classes.
These primitive data types are always lower case. All object types are uppercase.
So int x; is a primitive data integer. Integer y is an Integer object.
| Data Type Name | Size | Data Type | Range | Suffix character |
|---|---|---|---|---|
| int |
4 byte | integer type | -2,147,483,648 to 2,147,483,647 | --default-- no i or I |
| short | 2 bytes | integer type Do not use | -32,768 to 32,767 | no s or S |
| long | 8 bytes | integer type | -9,223,372,036,854,775,808 to 9,223,372,036,854,775,807 |
L |
| byte | 1 byte | integer type | -127 to +128 | no b or B |
| char | 2 bytes (because of Unicode) |
one character: 'a' or '\n'. Not "a" 'ab' or "ab" |
||
| float | 4 bytes | floating point / decimals Not used very often. |
3 .4e-45 to 3.4e+38 (8 decimal places) |
f or F |
| double | 8 bytes | floating point / real number | 1 .7e-324 to 1.7e+308 (16 decimal places) |
-- default -- d or D |
| boolean | 1 byte? | True/False (not equal to 1 or 0) |
You must add the correct letter at the end in order to specify something other than the default.
This means, whenever you use a FLOAT or a LONG, you have to write F or L.
For example, float depth = 1.235F; long startTime = 12345678L;
The other data types (byte, char, boolean) don't need suffix characters.
Strings are objects, but they act like primitive data types much of the time
| Integer | Floating Point | |
|---|---|---|
| divide by zero | crashes program | results in "infinity" |
| overflow (number too big) | wraps around to the biggest negative number | results in "infinity" |
| accuracy | exact | rounding errors |
| illegal math | only with doubles | Math.sqrt(-1) → NaN (not a number) divide 0 by 0 → NaN |
NOTE: if x is NotaNumber and y = x; y == x is still false. One NaN is never equal to another NaN!
Type in and run this program: MathExamples.java