A variable is a named memory location which temporarily stores data that
can change while the program is running.
A variable holds a value.
A final is a named memory location which temporarily stores data that
remains the same throughout the execution of the program.
It is a constant variable in the program.
The type of a variable indicates what kind of value it will
store. For example, the "type" may be mathematical in nature, such as an integer or decimal value, or it may be text or letters.
The name of a variable is known as its
identifier. You, the programmer, will choose the name of the variable.
A variable is given a value through an assignment statement.
Java recognizes different data "types" of
variables depending upon what kind of data they can contain.
Java has eight built-in primitive data types designated by reserved
words:
byte
short
int
long |
float
double
char
boolean |
Variables of different types occupy different amounts of
memory space and are described as having different sizes. |
Of the eight primitive data types in Java, the four most commonly used are: double, int, boolean, and char . When you learn about objects, you will discuss
the differences between primitives and objects.
Variables Most Often Used
Data Type |
Java Keyword |
Kind of Value |
Bytes of Memory |
Range of Values |
Character |
char |
1 character -
Unicode |
2 |
not
applicable |
Byte |
byte |
Integer |
1 |
-128 to127 |
Short integer |
short |
Integers |
2 |
-32,768 to
32,767
(-215 to 215 - 1) |
Integer |
int |
Integers |
4 |
-2,147,483,648 to 2,147,483,647
(-231 to 231 - 1) |
Long Integer |
long |
Integers |
8 |
-9223372036854775808 to
9223372036854775807
(-263 to 263 - 1) |
Float |
float |
Decimal
values to 7 decimal digit precision |
4 |
3.4e-38 to
3.4e38
positive and negative |
Double |
double |
Decimal
values to 15 decimal digit precision |
8 |
1.7e-308 to
1.73e308
positive and negative |
Boolean |
bool |
Boolean
(Logical) values
True or False |
1 |
not
applicable |
|
Rules for assigning
variables:
Assign int data types when you are
sure a variable is an integer (NO decimal points). (You could also use "short" or "long", but for now we will concentrate on "int". Which
type you choose would depend upon the size of the numbers.)
Assign double when decimals are
needed. (You could also use "float", but for now we will concentrate on "double".Which
type you choose would depend upon the size of the numbers.)
Assign char if the
variable will always contain only ONE character of data. A char variable is a single letter, number, or symbol and is always assigned using single quotes (char letter = 'M'; ).
Assign boolean if you are dealing with TRUE or FALSE situations. |
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