Computer Science 1, Section 3 Top Lectures Assignments Noticeboard  Defining classes - Part 2

Designing Classes

• Designing and developing classes is difficult!
• Can't do ad hoc
• Need a more systematic approach. Why?
• Don't waste time
• Reduce errors
• Allow others to re-use our code
• So, here's one approach (learn additional, more rigorous techniques in later courses)
1. Identify class(es)
2. Decide what behavior class will provide (informal)
3. Begin to specify prototypes, i.e., define its interface - interface to a class consist of set of methods that can be invoked on instances of class.
4. Write a sample program that uses the class - sometimes called a driver - helps us determine if design is sensible
5. Write skeleton class - class boilerplate, method prototypes, empty method bodies
6. Implement methods and test using driver.

Identify Classes

For example, developing program for a real estate office. House would probanly be appropriate class. (As might others of course.)
 

Identify Behavior

• Specify the style
• Specify the location
• Specify the asking price
• Return a description of the house
• Return a code for the house based on a given prefix
• Create a house
• Create a house based on another house
• ...

Interface and Prototypes

• class House
• public void setStyle (String theStyle)
• public void setLocation (String where)
• public void setPrice (String currentPrice)
• public String describe ()
• public String code (String prefix)
• public House () // no return type
• public House (House similarHouse) // no return type

Driver

class TryHouse {
    public static void main (String arg[]) {
	House someHouse = new House ();
	someHouse.setStyle ("Ranch");
	someHouse.setLocation ("Briarwood");
	someHouse.setPrice ("100000");
	System.out.println (someHouse.describe());
	anotherHouse = new House (someHouse);
    }
}

The Class Skeleton

  class House {
     public House () {
       //statements
     }
     public  House (House similarHouse) {
       //statements
     }
     public void setStyle (String theStyle) {
       //statements
     }
     public void setLocation (String where) {
       //statements
     }
     public void setPrice (String currentPrice) {
       //statements
     }
     public String describe () {
       //statements
     }
     public String code (String prefix) {
       //statements
     }
  // instance variables
}