• Administrative Notes:
  • Individual project 1 will be due on October 8.
  • Exam 1 will be on October 15. It will cover material from Chapters 2, 3, 4 (no graphics) and 5.
  • We will skip Chapter 4 for the moment.
  • Next Monday we'll do simple logic and simple if statements (sections 5.1 to 5.3). You will need this material to finish the very last part of Lab 4.
  • We will then spend several lectures practicing with designing programs using what we have learned so far.
  • It is very important that you master the mechanics of Labs 2 and 3 by the end of next week. There is plenty of assistance available next week specifically for this purpose.

• Formal syntax for items mentioned so far:
  • Method definition: (p. 61)
    Form: [visibility] resultType methodName ([argumentList]) { ... }
    Example: public int vectorLength(int x, int y) { ...}
    Interpretation: Method methodName returns a value of type resultType.
    

  • Method call: (p. 78)
    Form: [objectName.]methodName([argumentList])
    Examples:
           toSqYards(); // called within class definition
       aPiece.readSqYards(); // aPiece is an object identifier
       myVector.vectorLength(myX, myY); // myX is associated with the first parameter of vectorLength
    Interpretation: You don't have to put the objectName in front when the object calls its own methods.

  • Creating an object instance: (p. 76)
    Form: className variableName = new classConstructor([arguments]);
    Example:
            PieceOfFabric aPiece = new PieceOfFabric();
        VendingButton waterButton = new VendingButton("Make a selection", "Clear", "Push"); Interpretation: The className(...) on the right hand side specifies how the object should be built from its blueprint (class definition).

  • The return statement: (p. 80)
    Form: return expression;
    Example: return x + y;
    Interpretation: The return statement indicates the value to send back to the caller.

  • Assignment statement: (p. 83)
    Form: variable = expression
    Example: x = y + z*w;
    Interpretation: The variable on the left is assigned the value computed from the expression on the th right. (The expression on the right has to be of a compatible type.)

• Operators and Expressions:
  • Addition (+), subtraction (-), multiplication (*), division (/), and remainder (%).
  • Follow the rules of algebra. (We'll go through the precedence rules on p. 89 sometime next week.)

• An Example: Develop a class definition for an object representing a rational number (fraction).

  Specification: A fraction is the ratio of two integers, the numerator and denominator. In addition to being printed in the form a/b, a fraction give its value in decimal. Other operations that the fraction can perform are:

  • It can add another fraction to itself.
  • It can subtract another fraction from itself.
  • It can multiply another fraction times itself.
  • It can divide another fraction by itself.
  All of these operations change the fraction's value.

Contributed by a class member:
Did you hear that Sun recently created a new Java class of lawyers? Problem is, all they do is object...