1. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK1 Object-Oriented Programming Using Java Introduction to OOP

2. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK2 Programming Paradigms  Imperative Programming (C, Pascal, …)  Functional Programming (Lisp, ML, …)  Logic Programming (Prolog)  Concurrent Programming (Ada, Occam, …)  Object-oriented Programming (Smalltalk, C++, Java, …) –This is what we shall teach (through Java).

3. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK3 The Object-Oriented (OO) Programming Paradigm  Object-oriented Programming is one of the programming paradigms (school of thought, methodology) in computer science. Object Technology  Object-oriented Programming is well-known in the business world by the name of ‘Object Technology.’  Synonyms:Object == Instance == Entity Class ~= Static ~= Type

4. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK4 Why OOP?  Objects have two properties –fields (instance variables) and methods.  Fields tell you what an object is (properties).  Methods tell you what an object does (tasks).  Object oriented programming is alleged to have a number of advantages including: –Simpler, easier to read programs –More efficient reuse of code –Faster time to market –More robust, error-free code

5. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK5 Customer bill Customer michael Account peterSaving Objects  Our world is full of objects. Graphical representation of objects Object ‘type’ i.e. Class name Object name

6. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK6  Our world is full of objects. Graphical representation of objects Customer bill Objects Customer michael Account peterSaving

7. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK7 Modeling Our World  We try to model this object world.  Objects can accomplish tasks and keep data/state. –e.g. A drink dispensing machine sells Coke. It has a stock of 100 cans.  Inhuman?! –Certainly, but it helps us to program a computer in an organized and manageable manner.

8. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK8 Verbs and Nouns  Verbs  Action/ Task  Method  Nouns  Entity  Field A drink dispenser can sell coke, sell lemon tea. Its stock includes number of coke, number of lemon tea. It can deliver change.  Any implicit (or missing) verb/ noun?  Can you suggest a class name?

9. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK9 Classes  A class (e.g., Customer) is a kind of mold or template to create objects (e.g., michael and bill).  An object is an instance of a class. The object belongs to that class. Customer bill Customer michael Customer ‘instance-of’ Class Object

10. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK10 More Class Examples Person michael Person billGates Person Account johnCheque Account peterSaving Account

11. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK11 Object-Oriented Programming  We first define classes.  While the program is running, we may create objects from these classes.  We may store information in classes and objects.  We send messages to a class or an object to instruct it to perform a task. (For example, we send a deposit $250.00 message to an Account object to deposit $250.00 into the account.)

12. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK12 Account new Creating Objects  An object is created by sending a new message to a class. Method Message sent to Class Account: new (ask it to create a new Account object) Message sender An instance (new object) is returned to the sender main( ) Account johnSaving ‘instance-of’

13. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK13 Messages and Methods  An object consists of fields to store data and methods to manipulate the data. Account mySavingAC name Michael deposit withdraw … balance $123.45 Fields Methods Message: deposit $250.00 Argument of the message $250.00

14. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK14 Messages and Methods  A message may instruct an object to change the fields (state) of the object itself through a method. Account myAccount Account name Michael deposit withdraw … balance $123.45 yourAccount Account name Raymond deposit withdraw … balance $58.12 $250.00

15. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK15 Messages and Methods  A message may instruct an object to change the fields (state) of the object itself through a method. Account myAccount Account name Michael deposit withdraw … balance $373.45 yourAccount Account name Raymond deposit withdraw … balance $58.12

16. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK16 Messages and Methods  A method may return a value to the message sender. Account myAccount Account name Michael deposit withdraw … balance $373.45 $999.00

17. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK17 Messages and Methods  An object may return a value to the message sender through the method. Account myAccount Account name Michael deposit withdraw … balance $373.45 Result “ Failure ” Result “ Failure ”

18. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK18 Messages and Methods  Of course, we CANNOT send arbitrary messages to an arbitrary classes or objects. Account myAccount Account name Michael deposit withdraw … balance $373.45 rob $10,000.00 sell Coke deposit $30.00

19. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK19 Summary  Object-Oriented Programming (OOP) treats entities as objects, modeled by classes.  Objects and classes can –store data in fields and –perform actions in methods.

20. 2008-2009 1cMichael Fung, CS&E, The Chinese University of HK20 End Note  Readings and References –Preface –Chapter 1 Introduction  Exercise –1.1  Programming Projects –1.1, 1.2