1. Title Slide CSC 444 Java Programming Object Oriented Methodology By Ralph B. Bisland, Jr.

2. 2Internet Concepts What Is Object Orientation? A strategy for organizing systems as collections of interacting objects that combine data and behavior. Object Oriented Methodology –Object Oriented Design –Object Oriented Programming –Object Oriented Testing

3. 3Internet Concepts Developing Programs Procedural Method: Developer concentrates on developing code that mimics the procedure to represent the real world system. Object Oriented Method: Developer concentrates on developing representations of real world objects, their actions, and how they relate to each other.

4. 4Internet Concepts Objects An object is a software “bundle” of data and procedures that act on the data. A procedure is called a “method”. Objects are the heart of OOM. Objects share two common characteristics –State: What an object is currently “doing” –Behavior: What can an object do

5. 5Internet Concepts Example Of Objects A Lion : –States Color Weight Tired? Hungry? –Behaviors Sleep Hunt Roar

6. 6Internet Concepts Another Object A Car –States Current Speed Type of Transmission 2/4 Wheel Drive Lights On Current Gear –Behaviors Turning Breaking Accelerating

7. 7Internet Concepts One More A Baseball Player –States Batter Pitcher –Behaviors Batting Average Earned Run Average

8. 8Internet Concepts Pictorial View Of A Class Methods Data MessageResponse

9. 9Internet Concepts Objects An object is an instance of a class. Classes must be instantiated to produce objects. Examples: FordMustang = new Car ChevyCorvette = new Car Each object usually has different values for its instance variables.

10. 10Internet Concepts The Car Object Break Accelerate Steer Change Gears Toggle Lights 75 mph 4th Gear Lights On Methods Data

11. 11Internet Concepts Creating Objects To create an individual object, a class must be instantiated. Example: myCar=new Car (75mph, 4thgear, lightson) yourCar=new Car (60mph, 1stgrear, lightsoff) Use the methods to manipulate the instance variables. myCar.Accelerate(+15) yourCar.Accelerate(-10)

12. 12Internet Concepts Encapsulation The process of packaging an object’s data and methods together. Objects consist of a public interface (external) and a private (internal) section. The internal portion has more limited visibility than the external portion. Safeguards the object against unwarranted external access. Can only communicate with the object through its interface.

13. 13Internet Concepts Benefits Of Encapsulation Implementation Hiding : Protection of the internal implementation of object. The internal data and methods are the parts of the object hidden from other objects. Major benefit: Pata and methods can be changed without affecting other objects. Modularity: An object can be maintained independently of other objects. Also easier to distribute objects through the system.

14. 14Internet Concepts Messages How software objects interact and communicate with each other. Analogy: Two people communicating with each other. Person 1 to person 2: “Come here, please”. Sometimes the message must contain additional information. This is done through message parameters.

15. 15Internet Concepts Example Message: Accelerate the car by 15 mph. –The object to receive the message: car –The name of the action to perform: accelerate –Any parameters the method requires: 15 mph Message passing is accomplished through method calling. Messages and methods are synonymous. Messages can be sent to objects in another location: Distributed Object

16. 16Internet Concepts Classes A class is a template (or prototype) for an object. Analogy: A class is to an object is what a blueprint is to a house -- many houses can be built from the same blueprint. A blueprint outlines the makeup of a house. An object is an instantitation of a class. Classes can not be used by themselves. There may be many different instances of a class. Many cars, many lions, etc.

17. 17Internet Concepts Classes (ctd) Benefits of objects: modularity and information hiding. Benefits of classes: reusability. Each instance of a class has it’s own state variables, but share methods. State variables of the instance of a class are called “instance variables”.

18. 18Internet Concepts Inheritance What happens if an object is basically the same as other objects, but it has a few slight differences? Inherit the basic characteristics from a super class and form a sub class (AKA: parent-child classes). Inheritance: The process of creating a new class with the characteristics of an existing class, along with additional characteristics unique to the new class.

19. 19Internet Concepts Inheritance (ctd) When a subclass inherits from a superclass, it inherits all of the superclass state variables and the methods. Additional methods and/or state variables can be added to the subclass.

20. 20Internet Concepts Example Class: car Basic data –Number of wheels –Number of doors Types of Cars –Gas powered Fuel tank capacity MPG –Electric Powered Size battery

21. 21Internet Concepts Inherited Methods Inherited methods can be overridden Different code can be supplied in the methods for each subclass. Example: Gas powered cars can accelerate faster than electric powered cars, so the acceleration routine might be different.

22. 22Internet Concepts Another Example Class: Figure Rectangle –State Variables: Length, Width –Methods: Calculate_Area Circle: –State Variables: Radius –Method: Calculate_Area

23. 23Internet Concepts Inheritance Tree Car Gas PoweredElectric Powered 4-Cylinder 6-Cylinder

24. 24Internet Concepts Abstract Classes Sometimes it is useful to create superclasses that act purely as templates for more subclasses. The superclass serves as nothing more than an abstraction for the common class functionality shared by its subclasses. Called abstract classes. Abstract classes can not be instantiated - an object can not be created from it.

25. 25Internet Concepts Abstract Classes (ctd) Reason: Parts of it are yet to be defined. Parts of methods have yet to be implemented - abstract methods. The actual implementation of the method is defined in the subclass.

26. 26Internet Concepts Example Acceleration method can not be defined until the acceleration capabilities are known. –How a car accelerates is determined by the type of engine it has. –Engine type is unknown in the superclass –Child class would implement the specific acceleration method to reflect the acceleration capabilities of their respective engines.

27. 27Internet Concepts Another Example Class: Baseball Player Subclasses: Batter and Pitcher All baseball players have some basic data: Team, Uniform#, Birthdate, etc. All baseball players have some basic methods: ComputeAge, TaxComputations, etc.

28. 28Internet Concepts Another Example (ctd) Batters have some specific data: Atbats, Hits, Homeruns, etc. Batters have some specific methods: CalculateBattingAverage, CalculateSluggingPercentage, Etc. Pitchers have some specific data: NumbOfWins, NumbOfLosses, InningsPitched, EarnedRuns, etc. Pitchers have some specific methods: CalculateERA, etc.

29. 29Internet Concepts Example (ctd) Baseball Player Class Player Name, Team Name Uniform#, Birthdate CalculateAge CalculateTaxes Batter Subclass AtBats, Hits, HomeRuns CalculateBattingAverage, CalculateSP Pitcher Subclass NumberOfWins, NumberOFLosses, InningsPitched, EarnedRuns CalculateERA

30. 30Internet Concepts Example (ctd) It doesn’t make sense to create (instantiate) a Baseball Player object from the Baseball Player class (the abstract class). We must create an object of the subclasses, Batter or Pitcher (which inherits from the super class Baseball Player)

31. 31Internet Concepts Multiple Inheritance Enables a subclass to inherit characteristics from more than one superclass. Example: A whale inherits some characteristics from mammals and some from fish.

32. 32Internet Concepts Polymorphism Means “having many forms”. Describes an elegant and relative simple technique by which a reference that is used to invoke a method can actually invoke different methods at different times, depending upon the nature of the invocation. Accomplished by late binding of the class type to the method.

33. 33Internet Concepts Example Assume a superclass of “figure” which has a method called computeArea. Assume several subclasses of “figure”. Examples: Square, Triangle, Circle, etc. The method of computing the area of a figure is different for each different type of figure.

34. 34Internet Concepts Example (ctd) Since Square, Triangle, etc. are subclasses of figure, they can be assigned into figure. The method computeArea can be passed the value figure. figure = square (associated data) computeArea (figure) The correct method for computing the area is then executed because of late binding (binding at run time).