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 = =

6. 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?

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 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.

9. Characters & Booleans char boolean String
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.