Variables and Types
Variables allow us to store information such as numbers, words, or true/false expressions. A variable can be thought of as a box that stores information inside. In Java, variables are composed of three things: a name, type, and value.
Primitive Types
In Java we must specify what type of information we want our variables to hold. You must always give your variable a type before naming it, and specifying the value it holds. (Ex. int myVariable = 10;
)
Here are some of the primitive types found in Java:
Numeric Type:
As seen above, primitive numeric types in Java include both integers and doubles.
Integers are whole numbers, or counting numbers. (Ex. -5, -4, -3, -2, -1, 0, 1, 2, 3, 4, 5)
In Java we declare an integer using int
before the variable name. Here are a couple of examples:
int itemsInStore = 10;
int numberOfMessages = 8;
doubles are like integers, but can have decimals. (Ex. -54.34, 90.21, 0.1223)
In Java we declare a double using double
before the variable name. Here are a couple of examples:
double costOfApple = 1.24;
double milesToRun = 5.64;
Char Type:
Characters represent a single character.
In Java we declare a character using char
before the variable name. We also use single quotes to identify a character (Ex. 'A'
). Here are a couple of examples:
char currentGrade = 'A';
char favoriteLetter = 'W';
Boolean Type:
Booleans are variables that hold a true or a false value.
In Java we declare a boolean using boolean
before the variable name. Here are a couple of examples:
boolean passedCalculus = true;
boolean hasDog = false;
String Type:
Strings are variables that hold text. Strings are not a primitive type, so you must declare them using String
with a capital S. Unlike characters, we need to use double quotes when assigning strings (Ex. "This is my string."
). Here are a couple of examples:
String fishName = "Dog";
String myUniversity = "Arizona State University";
Naming Variables
Giving your variables meaningful names throughout your code is very important. Proper variable names allow others to easily read and understand your code. A good way to name your variables is to give them as descriptive of a name as possible, without making it too long. For example, int numberOfApplesOnTheTree = 10;
is a very long name, and can easily be replaced with a name like int numApples = 10;
.
Variable Naming Conventions:
Variable names must start with a letter,
$
symbol, or_
symbol.Variable names are case sensitive so
myVariable
is different thanMyVariable
Variable names, after the first character, can contain letters, numbers, or other characters.
Here are some examples of different variable names: