Java%20Primitives

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Java Primitives

• The Smallest Building Blocks of the Language
• (corresponds with Chapter 2)

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Terminology

• Primitive Data Type a category of data. A
  description of how the computer will treat bits
  found in memory.
• Variable a named location in memory, treated as
  a particular data type, whose contents can be
  changed.
• Constant a named location in memory, treated as
  a particular type, whose contents cannot be
  changed.
• Declaration the act of creating a variable or
  constant and specifying its type.
• Literal a hard-coded piece of data, part of the
  statement and not based on a variable or constant
  declaration.
• Operator a symbol that describe how to
  manipulate data and variables in memory
• Expression a combination of operators,
  variables, constants and/or literals that
  produces a resulting piece of data
• Assignment copying the results of an expression
  into a variable.
• Statement a program instruction telling the CPU
  what to do. (All statements end with semicolon).

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Java Primitive Data types

• boolean -- true/false
• char -- Unicode character (good for
  internationalization)
• byte -- 8-bit signed integer
• short --16-bit signed integer

• int -- 32-bit signed integer
• long -- 64-bit signed integer
• float -- 32-bit floating point number
• double -- 64-bit floating point nbr

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Identifiers

• Identifier the name of a variable, constant,
  class, or method
• Rules for using identifiers
• An identifier must start with a letter, an
  underscore, or a dollar sign.
• An identifier cannot contain operators, such
  as, -, and so on.
• An identifier cannot be a reserved word. (See
  Appendix A, Java Keywords, for a list of
  reserved words).
• An identifier cannot be true, false, ornull.
• An identifier can be of any length.

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Declaring Variables

• int x // declares x to be an
• // integer variable
• double radius // declares radius to
• // be a double variable
• char a // declares a to be a
• // character variable

Declaring multiple variables of the same
type datatype identifier1, identifier2,
identifier3
General format datatype identifier
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Assignment Statements

• x 1 // Assign 1 to x
• radius 1.0 // Assign 1.0 to radius
• a 'A' // Assign 'A' to a

General format VariableIdentifier expression
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Declaring and Initializingin One Step

• int x 1
• double d 1.4
• float f 1.4f
• char a a

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Constants

• final datatype CONSTANTNAME VALUE
• final double PI 3.14159
• final int SIZE 3

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Numeric Literals

• int i 34
• long l 1000000
• float f 100.2f orfloat f 100.2F
• double d 100.2d ordouble d 100.2D

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Common Types of Operators

• Assignment
• Arithmetic - /
• Comparison lt gt lt gt !
• Logical !

modulus
equals
not equals
Exclusive OR
AND
NOT
OR
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Modulus (remainder) Operator

• Modulus is very useful in programming. For
  example, an even number 2 is always 0 and an
  odd number 2 is always 1. So you can use this
  property to determine whether a number is even or
  odd. Suppose you know January 1, 2005 is
  Saturday, you can find that the day for February
  1, 2005 is Tuesday using the following
  expression

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Common Types of Expressions

• Arithmetic
• Combine numeric data with arithmetic operators
• Return a number
• Conditional
• Combine boolean values with logical operators
• Boolean values can be derived from comparison
  operators or boolean data values
• Returna boolean value

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Arithmetic Expressions

• 1 1
• x y
• 5 / 2
• 5 2
• radiusradius3.14159

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Sample Statements with Arithmetic Expressions

• //Compute the first area
• radius 1.0
• area radiusradius3.14159
• //Compute the second area
• radius 2.0
• area radiusradius3.14

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Arithmetic Expressions
is translated to (34x)/5 10(y-5)(abc)/x
9(4/x (9x)/y)
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Shortcut Operators
Operator Example Equivalent i8 i
i8 - f-8.0 f f-8.0 i8 i i8 / i/8 i
i/8 i8 i i8
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Increment andDecrement Operators

• x 1
• x x
• x-- --x
• y 2 x
• y 2 x
• y 2 x--
• y 2 --x

Add 1 to x
Subtract 1 from x
X is incremented after adding to 2
X is incremented before adding to 2
X is decremented after adding to 2
X is decremented before adding to 2
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Increment andDecrement Operators, cont.
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Integer vs. Floating Point Division

• When performing operations involving two operands
  of different types, Java automatically converts
  the operand of a smaller range to the data type
  of the larger range.
• Example
• 1/2 ? this will give 0 because both operands are
  integer
• 1.0/2 or 1/2.0 ? this will give 0.5 because
  the floating point literal is a double, so the
  integer literal (long) will be converted to a
  double thus floating point division will take
  place.

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Character Data Type

• char letter 'A'
• char letter '\u00041'
• char numChar '4'

Java uses Unicode instead of ASCII for character
data representation
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Character Escape Sequences
Backspace \b Tab \t Linefeed \n Carriage
return \r Backslash \\ Single quote \' Double
quote \"
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The boolean Data Type

• boolean lightsOn true
• boolean lightsOn false
• boolean test 11
• Returns true
• boolean test 12
• Returns false

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The symbol as concatenation operator

• System.out.println("The area is "
• area
• " for radius "
• radius)

String literals are enclosed in double quotes
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Boolean Operators Revisited
Operator Name ! not and or exclusive
or
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Truth Table for Operator !
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Truth Table for Operator
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Truth Table for Operator
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Truth Table for Operator
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Numeric Type Conversion

• Consider the following statements
• byte i 100
• long k i 3 4
• double d i 3.1 k / 2

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Conversion Rules

• When performing a binary operation involving two
  operands of different types, Java automatically
  converts the operand based on the following
  rules
•  
• 1.    If one of the operands is double, the other
  is converted into double.
• 2.    Otherwise, if one of the operands is float,
  the other is converted into float.
• 3.    Otherwise, if one of the operands is long,
  the other is converted into long.
• 4.    Otherwise, both operands are converted into
  int.

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Type Casting

• Implicit casting
• double d 3 (type widening)
• Explicit casting
• int i (int)3.0 (type narrowing)
• int i (int)3.9 (Fraction part is truncated)

Cast operator
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Operator Precedence

• Casting
• , --
• , /,
• , -
• lt, lt, gt, gt
• , !
• , , -, , /,

Parentheses can be used to override normal
precedence