• Arithmetic operators:
  • addition (+)
  • subtraction (-)
  • multiplication (*)
  • division (/)
  • remainder (%)

  Example: 5/2 has the value 2, while 5%2 has the value 1.

• Mixed-type expressions:
  • Arithmetic between two integers results in an integer.
  • Arithmetic in which at least one of the two operands is a double, gives a double.
  • In more complicated expressions, each operation is evaluated on the basis of its operand types.
  • You can type cast to change the type during the evaluation process. (e.g. putting (int) in front of an expression changes its type to integer.)

  Example: 5.0/2 is 2.5 as is 5.0/2.0 and 5/2.0. However 5/2 is just 2.

  Example: 4.0 + 5/2 is 6.0

  Example: (double)5/2 is 2.5

  Note: The conversion issue came up in our Fraction class when we were writing the GetDecimalEquivalent function. The expression myNumerator/myDenominator gave a truncated result. We needed to type cast at least one of the operands to get the decimal value.

• How are expressions evaluated?
  • Expressions inside parentheses done first. Nested parentheses are done inside to outside.
  • The order in which operators are evaluated is determined by their precedence (higher precedence before lower).
  • Operators of same precedence are evaluated left to right.
  • Consistent with the rules of algebra (but in Java there are more operators to worry about).

  Example: 4 + 6/2 is 7 not 5 because division has a higher precedence.

  Example: (double) 10/4 is 2.5 not 2 because type casting has a higher precedence.

• Common math functions are listed in Table 4.1 of the book:
  • Math.random() - return a random number in [0, 1).
  • Math.sqrt(x) - return the square root of x.
  • Math.PI - is the value of PI.
  • Math.E - the base of the natural log.
  • Math.NaN - represents an invalid number
  • pow(x,y) - return x^y if x > 0 and y is a positive integer.

  Example: Compute the area of a circle of radius r

        double myArea = Math.PI * r * r;
  

  Example: Return 0 or 1 at random:

       public int GetRandomToss() {
           return  (int) (2 * Math.random());
       }
  

  Example: Find the distance between the points (x1, y1) and (x2, y2)

       double dist = Math.sqrt(Math.pow(x1-x2, 2) + Math.pow(y1-y2,2)); 
  

Review: Quick-Check Exercises 1 to 6 on Page 168.

• The boolean is a primitive data type that evaluates to true or false.
• Use logical and (&&), logical or (||) and not (!) to make more complicated conditions.

Example: Write a boolean expression for testing whether X is between Y and Z inclusive.

       (Y <= X) && (X <= Z)

       X%2 == 0

       X <= 3

Review: Do Self-Check Exercises 1 to 4 on page 191.

Operator	Description	Examples
Method call	Request an object to perform an action	myButton.PushButton()
Type cast	Convert to specified type	(double)myNumerator
!, +(unary), -(unary)	Logical not, unary plus, unary minus	!myDone     or   -5 * -7
*, /, %	Multiplication, division, modulus (remainder)	9 * 10/3 % 2
+, -	Addition, subtraction	A + B - C
<, <=, >=, >	Relational inequality	A <= B
==, !=	Equal, not equal	A==B has value true or false
&&	Logical and	A && B is only true when both A and B are true.
||	Logical or	A || B is true when at lease one of A and B is true.
=	Assignment	A = B store the value of B into A

• x + y * z / w
• !((a > 5) || (c < (a + b)))