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) Characters (char)

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 Contains a standard ASCII character Contains a TRUE/FALSE value

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

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; A variable can be turned into a constant by adding the word final at the beginning of the declaration.

Unary Operators + Unary plus operator; indicates positive value (numbers are positive without this, however) - Unary minus operator; negates an expression ++ Increment operator; increments a value by 1 -- Decrement operator; decrements a value by 1 ! Logical compliment operator; inverts the value of a boolean

Operators Assignment operator Arithmetic Operators = Simple Assignment operator Arithmetic Operators + Additive operator - Subtraction operator * Multiplication operator / Division operator % Remainder operator

Order of Operations Order is determined by the precedence assigned to the operators in use within the expression. Example: 4 + 5 * 9 evaluates to 49 Still always use parenthesis!!!!…. even if it feels redundant.

Online resources http://java.sun.com/docs/books/tutorial/java/index.html