JAVA Variables
Variables store data that can vary throughout the program run. For example there may be several calculations done in your program where the answer of each calculation is set equal to the variable "x"
3+2 =x
4+6=x
8-2=x
Since each of the possible values for x above must be different, x is a variable, each time a calculation is done the current value of x may change.
Variables can also be set equal to text that changes as you run your program.
x = "Going"
x = "Gone"
Every variable in Java has both a name and a type
JAVA Variable Names
The name of a variable must contain only letters (upper and lower case), numbers (0 through 9), and the underscore _ character
The first character of a variable name cannot be a number
The variable name is case-sensitive so consistent use of upper and lowercase letters is a must
The variable names in Java can contain as many characters as you want
Variable names must not match reserved words already used by Java for other functions
x_1
string_x01
Answer_100
Are examples of acceptable variable names
Tip: Use a Capital letter to begin the name of a Class, use lowercase letters to begin a name of a variable or method
Tip: Make the name meaningful and descriptive to assist in remembering the functionality of the variable
JAVA Variable Types
The type for the variable helps to determine what kind of functions can be performed with that variable
Primitive Java Types
There are 4 number integer types (byte, short, int, and long)
Type int is the most common for integer whole numbers
0
-100
10000
There are 2 floating point number type (float and double)
Type double is the most common floating point / decimal number type
0.50
-6.75946
5.4e7
Single characters are stored with type char
'a'
'#'
'G'
True / False values can be stored with type boolean
true
false
Declaring Variables in Java
You need to type both the variable type and name to declare it in your JAVA code
int amountSpent;
The variables must be declared before you can use them in your code
If you have multiple variables using the same type you can separate them in the declaration using a comma
int numberOfpeople, servingsChicken, servingsBeef, servingsVeggie;
double priceChicken, priceBeef, priceVeggie;
Assigning values to Variables in Java
An assignment statement can be used in your code to assign a value to a variable after it has been declared. Assigning an initial value to a variable is done typically soon after the variable is declared.
numberOfpeople = 45;
priceChicken = 4.05 * numberOfpeople ;
The operation to the right of the equal sign is completed first, then the variable is defined / or redefined as in the example below
int counter_one;
counter_one=0; value is 0
counter_one = counter_one +1; value is 1
counter_one = counter_one +1; value is 2
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