Operators and Assignments - Arithmetic Operators

Additive operators (JLS §15.18)

• + and -
• have the same precedence and are left-associative
• operands must be primitive numeric types (see exception for String and +) or compile error occurs

Multiplicative operators (JLS §15.17)

• *, /, %
• have the same precedence and are left-associative
• operands must be primitive numeric types or compile error occurs;

Integer Division and Division by Zero (JJ pg 50, JLS §15.17.2)

• integer division rounds towards 0; ie result is truncated

      10 / 3 = 3;     // truncated result 
  

• if the value of the divisor in integer division is 0 an ArithmeticException is thrown

      10 / 0          // runtime error: ArithmeticException
  

• if the value of the divisor in floating-point division is 0 no exception is thrown; the value of the results are as follows:
  • division of a positive floating-point value: POSITIVE_INFINITY
  • division of a negative floating-point value: NEGATIVE_INFINITY
  • division of a floating-point value by -0: POSITIVE_INFINITY

    10.34 /  0           // result:  Infinity
   -10.34 /  0           // result: -Infinity    
    10.34 / -0           // result:  Infinity
     0    /  0           // result:  NaN (Not a number) 

Modulo operations (JLS §15.17.3)

• the modulo operator % is also called the remainder operator as it returns the remainder, or fractional part, of a division operation
• x % y is equivalent to x - ((int) (x/y) * y)
• can be used with both integer and floating-point numbers
• following rules apply as to the sign of the result:
  • result is negative if the divdend is negative
  • result is positive if the divdend is positive
  • if the divisor is zero, a runtime ArithmeticException is thrown
  • if the dividend is a floating-point value and the divisor is zero, no exception is thrown and the result is NaN

      5 % 3  =  2
     -5 % 3  = -2
    5.0 % 3  =  2.0
   -5.0 % 3  = -2.0 
    5.0 % 0  = NaN              // not a number

Also see:

• Binary numeric promotion
  
• Overflow and underflow
  
• Sun Tech Tip: Division by Zero

Example Code

TestArithmetic.java

Traps

• floating point operation throwing an ArithmeticException