Primitive Variables

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Primitive Variables
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Whats 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

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Whats 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, )

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JAVAs Primitive Variables

• Binary Value (boolean)
• Numbers
• Integer (byte, short, int, long)
• Real Numbers (float, double)
• Characters (char)

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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

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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?

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Why so many?

• Its 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.

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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.

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Characters Booleans

• char
• Contains a standard ASCII character
• boolean
• Contains a TRUE/FALSE value

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Declaration

• variable_type variable_name
• Example
• int x
• double temperature
• char initial
• boolean light

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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

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JAVA keywords
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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)

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Example

• If we wanted to have a double that stores the
  rooms temperature
• The Good
• double roomTemperature
• The Bad
• double ZED
• double theTemperatureInOurComputerRoomOnSeptemberT
  heTenth
• The Ugly (Illegal)
• double case
• double room Temperature
• double 9/10/07Temperature

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Initialization

• Variables can be initialized when they are
  declared
• int butterbeerBottles 99
• double bodyTemperature 98.6
• char display a
• boolean light false
• A variable can be turned into a constant by
  adding the word final at the beginning of the
  declaration.

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Unary Operators

• Unary plus operator indicates positive value
  (numbers are positive without this, however)
• - Unary minus operator negates an expression
• Increment operator increments a value by 1
• -- Decrement operator decrements a value by 1
• ! Logical compliment operator inverts the
  value of a boolean

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Operators

• Assignment operator
• Simple Assignment operator
• Arithmetic Operators
• Additive operator
• - Subtraction operator
• Multiplication operator
• / Division operator
• Remainder operator

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Order of Operations

• Order is determined by the precedence assigned to
  the operators in use within the expression.
• Example 4 5 9 evaluates to 49
• Still always use parenthesis!!!!. even if it
  feels redundant.

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Online resources

• http//java.sun.com/docs/books/tutorial/java/index
  .html