Primitive Variables

What’s a Variable? A quantity or function that may assume any given value or set of values (source – Dictionary.com) What types of values have we assigned to variables in mathematics and science? Integers and Real Numbers Temperature and Weight Names and Places

What’s a Primitive? Being the first or earliest of the kind or in existence Given just one group of binary digits, what types of things could we come up with? A Binary Value (True/False) Numbers (1, 4, 21) Characters (A, k, &)

JAVA’s Primitive Variables Binary Value (boolean) Numbers Integer (byte, short, int, long) Real Numbers (float, double) Character (char) Text (String) – not a regular primitive variable!

Why so many Integer names? Each one consists of a different number of bits. For example, a byte consists of 8 bits and holds a value from –128 to 127. Calculate 28 = 128 + 127 + 1 =

The other Integer Variables short Occupies 16 bits or 2 bytes int Occupies 32 bits or 4 bytes long Occupies 64 bits or 8 bytes Can you guess the range of values each one stores?

Why so many? It’s a tradeoff The greater number of bytes each one stores, the greater the range of values it can represent. But the larger number of bytes used put more demand on memory resources.

Real Numbers float double Occupies 32 bits or 4 bytes, with 6 or 7 significant digits. double Occupies 64 bits or 8 bytes, with 14 or 15 significant digits.

Characters & Booleans char boolean String Contains a standard ASCII character boolean Contains a TRUE/FALSE value String Contains a line of text

AP Exam The only ones that you need to be familiar with for the AP Exam are: int double boolean char String

Declaration variable_type variable_name; Example: int x; double temperature; char initial; boolean light; String sentence;

Naming Rules Must start with a letter, underscore(_), or dollar sign($) After 1st letter, you can use numbers Can NOT be a JAVA keyword White Space is not permitted (space). No Special Characters They are case sensitive so “BOX” is not the same name as “box”

JAVA keywords

Naming Convention The first letter of the variable is lower case. When using more than one word in the variable name, the first letter of each word after the first is capitalized. Be descriptive (to a limit)

Example If we wanted to have a double that stores the room’s temperature: The Good double roomTemperature; The Bad double ZED; double theTemperatureInOurComputerRoomOnSeptemberTheTenth; The Ugly (Illegal) double case; double room Temperature; double 9/10/07Temperature;

Initialization Variables can be initialized when they are declared: int butterbeerBottles = 99; double bodyTemperature = 98.6; char display = ‘a’; boolean light = false; String insult = “You Strink!”; A variable can be turned into a constant by adding the word final at the beginning of the declaration.