Primitive Data Types

1
Primitive Data Types

• There are a number of common objects we encounter
  and are treated specially by almost any
  programming language
• These are called basic (primitive) objects, such
  as integers etc
• E.g., Java predefines classes for such basic
  types
• for example, one predefined class is Integer

To create an Integer (object) Integer
wagePerHour new Integer(10)
System.out.println( wagePerHour )
2
Primitive Data Types

• Although in pure object-oriented languages (such
  as Smalltalk and Ruby), we can consider
  everything as objects and defines everything as
  class, for efficiency, some languages like C
  and Java treat common objects such as numbers,
  characters, and logical values specially, and
  introduces them into the language as primitive
  data types
• Note this division between primitive types and
  objects is disliked by some programmers familiar
  with languages such as Smalltalk and Ruby where
  everything is an object

3
Primitive Data Types

• There are exactly eight primitive data types
• four of them represent integers
• byte, short, int, long
• two of them represent floating point numbers
• float, double
• one of them represents characters
• char
• and one of them represents boolean (logical)
  values
• boolean

4
Numeric Primitive Data Types

• byte, short, int, long, float, and double are
  numeric data types
• The difference among the various numeric
  primitive types is their storage sizes and
  representations, and therefore the ranges and
  precision of the values they can store
• To understand this, we need to have a rough
  understanding of computer memory storage

5
Memory
Primary storage area for programs and data Also
called RAM
RAM is divided into many cells each cell can be
identified by a numeric address
Main Memory
9278 9279 9280 9281 9282 9283 9284 9285 9286
- how many values can a byte represent?
- how many values can 2 bytes represent?
6
Numeric Primitive Data

• Objects of different numeric data types occupy
  different number of cells

IEEE 754format
7
Characters

• A char is a single character from a character set
• A character set is an ordered list of characters
  each character is given a unique number
• Character literals are represented in a program
  by delimiting with single quotes
• 'a 'X '7' ' ',' '\n'

8
Character Sets

• The ASCII character set is quite popular. It
  includes

9
Boolean

• A boolean value represents logical value true or
  false
• The reserved words true and false are the only
  valid values for a boolean type
• A boolean can also be used to represent any two
  states, such as a light bulb being on or off

10
Variables Revisited

• We already know that a variable must be declared,
  specifying the variable's name and the type of
  information that will be held in it
• As of now, think of a variable as a name for a
  location in memory cell (we will revisit the
  concept later)

11
Variables

• A variable can be given an initial value in the
  declaration

int sum 0 int base 32, max 149 String
msg1 new String( Hello ) String msg2
Hello

• When a variable is referenced in a program, its
  current value is used

12
Change the Value of a Variable Assignment
Statement

• An assignment statement changes the value of a
  variable
• The assignment operator is the sign

• The expression on the right is evaluated and the
  result is stored in the variable on the left

• The value that was in total is overwritten

• Remember you can only assign a value to a
  variable that is consistent with the variable's
  declared type

13
Constants

• A constant variable is an identifier that is
  similar to a variable except that it holds one
  value for its entire existence
• Why constants
• give names to otherwise unclear literal values
• facilitate changes to the code
• prevent inadvertent errors
• The compiler will issue an error if you try to
  assign value to a constant variable after its
  declaration

14
Arithmetic Expressions

• An expression is a combination of operators and
  operands
• Arithmetic expressions (we will see logical
  expressions later) are essentially special
  methods applied to numerical data objects
  compute numeric results and make use of the
  arithmetic operators

Addition Subtraction - Multiplication Divis
ion / Remainder
15
Division and Remainder

• If both operands to the division operator (/) are
  integers, the result is an integer (the
  fractional part is discarded)

14 / 3 equals?
8 / 12 equals?

• The remainder operator () returns the remainder
  after dividing the second operand into the first

14 3 equals?
8 12 equals?