CS 303E Class 11: Boolean Logic, Boolean Expressions, and more on if statements'

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CS 303E Class 11Boolean Logic, Boolean
Expressions, and more on if statements.
So logically If she ways the same as a duck
she's made of wood ..and therefore A
WITCH!!!!! - Monty Python and the Holy Grail
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The Tax Rate Problem

• Last time we calculated tax rates according to
  marital status and income.
• A series of nested if - else statements was
  needed to assign the correct tax rate
• if(status SINGLE)
• if(income lt 21450)
• taxRate 0.15
• else if(income lt 51900)
• taxRate 0.28
• else
• taxRate 0.31
• else
• if(income lt 35800) // and so forth

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An Alternate Approach

• Like, most programming languages, Java contains
  another way of determining an outcome based on
  more than one condition.
• The conditions we saw last time are example of
  boolean expressions
• A boolean expression is an expression that
  evaluates to true or false
• if( x gt 10)
• There is another primitive data type in Java,
  boolean
• The equals method return type is boolean

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Logical Operators

• There are three boolean operators that allow us
  to create more complex conditions
• Logical AND, both condition must be true
  for the whole expression to be true
• if(status SINGLE income lt 21450)
• Logical OR, if one or both of the conditions
  is true the whole expression is true
• if(month APRIL month JUNE month
  SEPTEMBER month NOVEMBER)
• daysInMonth 30
• ! Logical NOT, gives the opposite of the
  condition

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Boolean Logic

• If A and B are conditions (A is x lt 10, B is y gt
  5 for example) then the following are the truth
  tables for our three logical operators

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Complex Mathematical Checks

• Now we can create a programming language version
  of the check x lt y lt z
• if( x lt y y lt z)
• Style issues
• Put a space before and after the comparison
  operators and logical operators.
• Parenthesis may be used to contain each simple
  condition.
• if( (x lt y) (y lt z) )

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Complex Boolean Expressions

• You can piece together as many conditions as
  desired with whatever logical operators are
  desired to create very complex boolean
  expressions
• Precedence of Logical operators
• ( ) parenthesis
• ! logical NOT
• logical AND
• logical OR
• If an expressions value is known from a condition
  early the rest of the expression is not evaluated
• if(month APRIL month JUNE month
  SEPTEMBER month NOVEMBER)
• daysInMonth 30

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Creating Complex Boolean Expressions

• Complete the following methods in the Student
  class
• public String cluelessnessLevel
• A student is "completely clueless" if they are a
  freshmen with a major besides business or a
  graduate student
• A student is "clueless" if they are are a
  freshmen majoring in business or a sophomore or a
  computer science major and not a senior
• A student is "a little clueless" if they are a
  junior or an education major.
• A student is "informed" if they are a senior, but
  not a computer science major and not in the
  business school
• A student is "informed" if they are a senior in
  the business school

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More methods

• Complete a method sittingInTraffic which returns
  true if a students commute is greater than 2
  miles and they do no have a car or their commute
  is over 10 miles and they do have a car
• Complete a method bumming, which returns true if
  a student is a freshmen or a computer science
  major and taking 15 or more hours this term or
  the hardest class this term is CS303e

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More Methods

• Write a method estimatedGPA which returns a
  double base on the following
• All freshmen students' estimated GPA is 3.0
• All students in the college of Engineering and
  students in Natural Science majoring in math,
  chemistry, or computer science have an estimated
  GPA of 2.75
• All students in the college of liberal arts and
  education have an estimated GPA of 3.95
• Everyone else's GPA is estimated to be 3.5

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boolean types

• Variables of type boolean may be declared
• boolean happy true
• true and false are reserved words in Java
• boolean variables may be used where a boolean
  expression may be used.
• boolean variables may also be assigned the value
  of a boolean expression
• happy (hours lt 12) (year ! FRESHMEN)