1. Primitive Variables

2. 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

3. 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, &)

4. 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!

5. 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 =

6. The other Integer Variables • shortOccupies 16 bits or 2 bytes • intOccupies 32 bits or 4 bytes • longOccupies 64 bits or 8 bytes • Can you guess the range of values each one stores?

7. 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.

8. Real Numbers • 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.

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

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

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

12. 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”

13. JAVA keywords

14. 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)

15. 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;

16. 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.