 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.