Using Variables

Declare variable data type
Declare variable name

1int 2width;
int height;

Why Declare Variables?

Before we use a variable, Java needs to know about the variable (it's data type).

We can use the highlighted width variable only because we have declared it before using it.

Java is a strongly typed language

int width;
int height;

//Use variable "width"
width = 10;

Declare Then Use

Declare variable
Use variable

Java executes code sequentially forward or top-down

1int width;
int height;

2width = 10;

This Will Not Work

This fails. The variable width is used before it is declared.

Use variable (incorrect - used before declared)
Declare variable (incorrect - declared after used)

1width = 10;

2int width;

Example

First we declare variables.

Then we use the variables.

Java is happy because when we use the vars it already knows about them (via the declarations)

int width;
int height;
int sum;

width = 10;
height = 5;
sum = width + height;