A quantity or function that may assume any given value or set of values What types of values have we assigned to variables in mathematics and science? (source – Dictionary.com) Integers and Real Numbers Temperature and Weight Names and Places 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, &) Binary Value (boolean) Numbers Integer (byte, short, int, long) Real Numbers (float, double) Character (char) Text (String) – not a regular primitive variable! 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 = 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? 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. float 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. char Contains a standard ASCII character boolean Contains a TRUE/FALSE value String Contains a line of text The only ones that you need to be familiar with for the AP Exam are: 1. int 2. double 3. boolean 4. char 5. String variable_type variable_name; Example: int x; double temperature; char initial; boolean light; String sentence; 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” abstract assert boolean break byte case catch char class const continue default do double else enum extends final finally float for goto if implements import instanceof int interface long native new package private protected public return short static strictfp super switch synchronized this throw throws transient try void volatile while 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) 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 double double case; room Temperature; 9/10/07Temperature; 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.