• Creating Classes:
  • Writing an intensive definition of a set (i.e., a definition that is written in terms of the properties of the elements)
• Using Objects:
  • Establish an identity (in a declaration statement)
  • Allocate memory and initialize the attributes (using the new operator)
  • Invoke methods on the object (using the . operator with the object identifier as the right-side operand)
• Using Classes:
  • Use accessible class attributes or class methods (using the . operator with the class identifier as the right-side operand)

• An Observation:
  • The . operator requires an object or class identifier as the left-side operand
• A Question:
  • What should the left-side operand be when writing the class (i.e., inside of the class definition)?
• The Answer:
  • this (which is a reference to the owning object)

Why are some attributes static and some not?
What are the formal parameters of the constructor?
What local variables are used in the constructor?
What methods are invoked in the constructor and are they static or not?

How do you refer to the owning object?
Why isn't it necessary to do so?
Could you do so anyway?

Which new methods are private?
What is true of private members?
Why include private methods?
Is it necessary to use this. when invoking private methods?
Which members are static and which are not?

How many objects are being compared?
How are they referred to?
Is it necessary to use this.?
Why are the attributes of other accessible?

When might this method be useful?
What operators are being used?

• Three Related Questions:
  • What happens if you use a non-static member in a static method, why, and when?
  • public class Interval { private double left, right; public Interval(double left, double right) { this.left = left; this.right = right; } // What's happens here, why, and when? public static double getLength() { return this.right - this.left; } }
• Another Question:
  • How do you fix this problem? (Hint: The answer is not to behave like 10,000 monkeys at 10,000 keyboards!)

• Where Else Beginning Programmers Often Encounter This:
  • In the main() method of the main class
  • public class Game { private int lives; // What's happens here and why? (And when?) public static void main(String[] args) { lives = Integer.parseInt(args[0]); } }
• Another Question:
  • How do you fix this problem? (Hint: Again, the answer is not to behave like 10,000 monkeys at 10,000 keyboards!)

• Is It Possible?
  • Yes, because static members belong to the class (i.e., the set) and hence to individual elements
• Is It A Good Idea?
  • No, it's confusing and there is no advantage to doing so

• The Owning Object:
  • In Python, the owning object is often named self (though needn't be) and is the first parameter passed to a method
• Class and Static Methods:
  • Python makes a disctinction between class methods and static methods