# 3.13. Variables - Summary¶

In this chapter you learned about the three primitive types on the exam: `int`, `double`, and `boolean`. You also learned how to declare (name) and change the value of variables. You learned about operators, casting, and integer constants for the min and max integer values. You also learned how to create a random number.

## 3.13.1. Concept Summary¶

• Boolean - An expression that is either `true` or `false`.

• Camel Case - One way to create a variable name by appending several words together and uppercasing the first letter of each word after the first word (`myScore`).

• Casting a Variable - Changing the type of a variable using (type) name.

• Double - A type in Java that is used to represent decimal values like -2.5 and 323.203.

• Declare a Variable - Specifying the type and name for a variable. This sets aside memory for a variable of that type and associates the name with that memory location.

• Initializing a Variable - The first time you set the value of a variable.

• Integer - A whole number like -32 or 6323.

• Modulus - The `%` operator which returns the remainder from one number divide by another.

• Operator - Common mathematical symbols such as `+` for addition and `*` for multiplication.

• Random Number - A random number picked from a range of numbers. Used in games to make the game more interesting.

• Shortcut Operators - Operators like `x++` which means `x = x + 1` or `x *=y` which means `x = x * y`.

• Variable - A name associated with a memory location in the computer.

## 3.13.2. Java Keyword Summary¶

• boolean - used to declare a variable that can only have the value `true` or `false`.

• double - used to declare a variable of type double (a decimal number like 3.25).

• false - one possible value for a boolean variable.

• int - used to declare a variable of type integer (a whole number like -3 or 235).

• static - means that the field or method exists in the object that defines the class.

• true - one possible value for a boolean variable.