Variables

Variables are elements in code that can store data.

Data Types

Data in Java have data types to help differentiate objects from each other. There are two general categories of data types— Primitives and Composites. We'll go over commonly used data types here.

Primitives

Primitives are simple data types that don't take up a lot of data and are generally very simple.

Data Type	Description	Example(s)
Integer (int)	Whole numbers, no decimals.	int num = 1;
Doubles	numbers with decimals. Also known as floats.	double num = 0.24;
Characters (chars)	Digits, icons, or letters. Note that a digit's value is different from what it looks like.	char c = 'A'; char fourAsDigit = '4'; (not the same as the number 4)
Booleans	Conditions, used for logic	boolean incomingTest = true; boolean studying = false; boolean correctMath = (2 == 4); // true

Composites

Composites generally are made from groups of smaller primitives. Due to their complexity, (except for strings) they are treated differently by the computer. Here are some noticeable ones:

Data Type	Description	Example(s)
Strings	Store text (multiple chars)	string intro = "Hello World!"
Arrays	Store multiple values of the same type	int[] array = {5, 4, 3, 2, 1} char[] msg = {'H', 'E', 'L', 'P'}
User-Created Data Types	Don't worry about this— we'll cover it later. Its fields and purposes could change depending on what it's used for.	Object o = new Object() Animal cat = new Animal("Cat");

Creating & Modifying Variables

All you need to do is define a variable name and set its data type. It's that simple.

[data type] variableName;
/* example */
int number;

Variables are kinda useless if you can't assign them values. To do this, just set the variable's name to some value, like so:

int number = 3;
/* you could also do this */
int number;
number = 3;

Note that you can only assign variable values the same type as the variable or your code will break. For example, you can only set variables that have a data type of "String" strings.

However, there are some exceptions to this— doubles and integers. If you assign an integer variable a double, it would just round down that value and set that whole number to an integer.