A variable is a named memory location which temporarily stores data that can change while the program is running.
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.
The name of a variable is known as its identifier.
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.
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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 short, int or long data types when you are sure a variable is a whole number (NO decimal points). Which type you choose depends upon the size of the numbers.
Assign float or double when decimals are needed. Which type you choose depends upon the size of the numbers.
Assign char if the variable will always contain only ONE character of data.
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