Logical Operators

1
Logical Operators

• Computer Science
• Chapter 5

2
Logical Operators

• Logical Operators are used in Java similar to the
  way they are used in English.

3
Logical Operator AND

• AND is represented by a double ampersand ()
• Evaluates two separate conditions
• Evaluates to true only if both conditions
  evaluate to true
• if (( x gty) (xlt100)) // then take action

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Logical OR Operator

• Or operator is represented by
• Evaluates two conditions
• Will evaluate to true is either condition is true
• if ( (xgty) (xlt100) if x is greater than y or
  x is less than 100, take action

5
Logical NOT

• Logical NOT is represented by !
• Evaluates to true if the expression is false
• if ( !(xgty)) // if x is not greater than y take
  action

6
Truth Tables

• Truth tables are often used to map the results of
  logical operations.

7
Short Circuit Evaluation

• The Java Virtual Machine evaluates from left to
  right.
• AND Operator
• First expression evaluates to false
• Second statement will not be evaluated because
  both need to be true
• This is called short circuit evaluation

8
Division By Zero

• Trying to divide a value by zero will generate an
  error
• Take advantage of short circuit evaluation
• first testing the divisor to see if it is equal
  to zero
• if ((yValue ! 0) ( ( xValue / yValue)lt100))
  // the complete action

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Short Circuit Evaluation OR Statement

• If the left side of an OR statement is true
• The right side does not need to be evaluated
• Only one side of the expression has to be true
  when using the OR operator
• if (amountRequestedgt 300 amountRequestedgt
  getBalance())
• displayErrorBox()