• Definitions:
  • An operator is a symbol indicating that an operation is to be performed on one or more operands
  • An operand can be a variable, literal, or expression
• Number of Operands:
  • A unary operator has one operand
  • A binary operator has two operands
• Values:
  • Boolean values can be either true or false
  • Integer and floating-point numbers are both considered numeric values

• Infix Notation for Binary Operators:
  • Operand Operator Operand
• Postfix Notation for Binary Operators:
  • Operand Operand Operator
• Prefix Notation for Binary Operators:
  • Operator Operand Operand

• Other Names:
  • Prefix Notation is sometimes called Polish Notation
  • Postfix Notation is sometimes called Reverse Polish Notation
• Resulting Humor(?):
  • 
    (Courtesy of xkcd)

• Operands:
  • Numbers (or types that can be converted to numbers)
• Result:
  • A Boolean

• The Big Four:
  • Greater than: >
  • Less than: <
  • Equal to: ==
  • Not equal to: !=
• Two More:
  • Greater than or equal to: >=
  • Less than or equal to: <=

• Involving Literals:
  • 7 < 5
  • 3 == 3
  • 7 != 7
• Involving Variables (Declared Elsewhere):
  • this_variable < that_variable
  • this_variable >= 15
  • (x + y) != (a * b)

• Use as Expected:
  • byte
  • short
  • int
  • long
• Use with Care (Because of Rounding Issues):
  • float
  • double
• Don't Use:
  • Reference types (e.g., String)

• An Observation:
  • The == and != operators can be used with boolean operands
• However:
  • Don't - doing so is inelegant

• The Inelegant Expressions:
  • x == true
  • y == false
• Why They Are Inelegant:
  • x == true and x evaluate to exactly the same thing
    (i.e., when x evaluates to true it follows that x == true evaluates to true, and when x evaluates to false it follows that x == true evaluates to false)
  • y == false and !y evaluate to exactly the same thing
    (i.e., when y evaluates to true it follows that !y evaluates to false and y == true evaluates to false, and when y evaluates to false it follows that !y evaluates to true and y == false evaluates to true)
• An Analogy:
  • Using them is like using a + 0 instead of a and almost all style guides prohibit their use

• An Observation:
  • Since relational operators evaluate to a boolean value they can be "combined" using logical operators
• An Example:
  • (gpa >= 2.0) && (credits >=120)

Which of the following expressions are syntactically correct?

a > 0 && < 100

10 < 63 < 105

10 < 63 && 10 < 105
  

Which of the following assignment statements are syntactically correct?

boolean    a, b;
int        i, j;

a = i < j;
b = a && b;
i = i + j;
i = i < j;
b = a && ((i == j) || (i > j));