a quantity or function that may assume any given value or set of values (source – dictionary.com)...
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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 NumbersTemperature and WeightNames 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.
Calculate28 = 128 + 127 + 1 =
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?
It’s a tradeoffThe 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.
floatOccupies 32 bits or 4 bytes, with 6 or 7
significant digits.double
Occupies 64 bits or 8 bytes, with 14 or 15 significant digits.
charContains a standard ASCII character
booleanContains a TRUE/FALSE value
StringContains a line of text
The only ones that you need to be familiar with for the AP Exam are:
1. int2. double3. boolean4. char5. 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 numbersCan NOT be a JAVA keywordWhite Space is not permitted (space).No Special CharactersThey are case sensitive so “BOX” is not the
same name as “box”
abstract continue for new switchassert default goto package synchronizedboolean do if private thisbreak double implements protected throwbyte else import public throwscase enum instanceof return transientcatch extends int short trychar final interface static voidclass finally long strictfp volatileconst float native super 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 Gooddouble roomTemperature;
The Baddouble ZED;double theTemperatureInOurComputerRoomOnSeptemberTheTenth;
The Ugly (Illegal)double case;double room Temperature;double 9/10/07Temperature;