Object-Oriented Programming Basics: Objects, Classes, Messages & Methods

1. Object, Class, Message & Methods OOP

2. Objects • Object attribute definition allows for object to have independent attribute values. Ex: Benjamin & Bernie are customers of HomeCare share some similar information like a name, an address, & a budget. • Beside attribute, object also have some method. Ex: Benjamin & Bernie as customers have some behaviour like making purchase.

3. Object Structure Benjamin as an object: attributes: name=“Benjamin” address=“1, Robinson road” budget=“2000” methods: purchase() {send a purchase request} getBudget() {return budget}

4. Object Structure Bernie as an object: attributes: name=“Bernie” address=“18, Sophia road” budget=“1000” methods: purchase() {send a purchase request} getBudget() {return budget}

5. Class • A Class is a definition template for structuring and creating objects with the same attributes and methods. • Ex: Like Benjamin & Bernie, All customers of HomeCare share the same set of attribute & method definition. They all have attributes: name, address & budget, and methods purchase() & getBudget().

6. Class Class Customer: attributes: name address budget methods: purchase() {send a purchase request} getBudget() {return budget}

7. Object vs class • One major difference between object & class is in the way are treated in objects & class. • A Class  attributes & methods are declarations that do not contain values. • An Object  are created instances of a class that has it own attributes & methods (state).

8. Object & Class • Examine :Object & Class at salesperson

9. Object Structure Sean as an object: attributes: name=“Sean” methods: takeOrder() { check with the warehouse on stock abailability check with the warehouse on delivery schedule if ok then{instruct warehouse to deliver stock(address, date) return ok else return not ok}

10. Class Class Salesperson: attributes: name methods: takeOrder() { check with the warehouse on stock abailability check with the warehouse on delivery schedule if ok then{instruct warehouse to deliver stock(address, date) return ok else return not ok}

11. Message & Method • Objects communicate with one another by sending messages. • A messages is a method call from a message-sending object (sender) to a message-receiving object (receiver). • An object responds to message by executing one of its methods. • Such parameter allows for added flexibility in message passing. • Offcourse, an object may have as many methods as required.

12. Message Components • A message composed of: • An object identifier. • A method name. • arguments (parameter). • Ex: Benjamin sent a messages to Sean when Benjamin wanted to buy a sofa set. The reasonable location is in Benjamin’s purchase() method

13. Message components Benjamin as an object: attributes: name=“Benjamin” address=“1, Robinson road” budget=“2000” methods: purchase( Sean.takeOrder(“Benjamin”, “Sofa”,”1, Robinson Road”, “12 September 2012”) getBudget() {return budget} Sean is receiver of the message takeOrder is method call on Sean Reds are arguments of message

14. Method • A message is valid if the receiver has a method that corresponds to the method named in message & the appropriate arguments. • Ex: the takeOrder() message is valid because Sean has a corresponing method & the required arguments.

15. Object Structure Sean as an object: attributes: name=“Sean” methods: takeOrder(who,stock,address,date) { check with the warehouse on stock abailability check with the warehouse on delivery schedule if ok then{instruct warehouse to deliver stock to address on date return ok else return not ok}

16. Creating Objects • Objects are created from classess. • Created object instances are individuals with their own state. • Ex: Counter

17. First Object First Counter Object Attributes: number = 10 Methods: add() {number = number + 1} initialize() {number = 0} getNumber() {return number}

18. Second Object SecondCounter Object Attributes: number = 2 Methods: add() {number = number + 1} initialize() {number = 0} getNumber() {return number}

19. Third Objek ThirdCounter Object Attributes: number = 7 Methods: add() {number = number + 1} initialize() {number = 0} getNumber() {return number}

20. Class Counter Class Counter Attributes: number Methods: add() {number = number + 1} initialize() {number = 0} getNumber() {return number}

21. Summary • Objects are defined by classes. • Objects from the same class share the same definition of attributes and methods. • Objects from the same class may not have the same attribute values. • Objects from different classes do not share the same definition of attributes or methods. • Objects created from the same class share the same definition of attributes and methods but their state may differ. • A method is a set of operations executed by an object upon the receipt of a message. • A message has three components: an object identifier, a method name and arguments. • A message-receiving object is a server(receiver)to a message-sending object known as a client(sender).