OBJECTORIENTED PROGRAMMING Mimi Opkins CECS 277 Objects Are

OBJECT-ORIENTED PROGRAMMING Mimi Opkins. CECS 277

Objects Are Black Boxes Message Code Data Message

Objects are Building Blocks

Objects and Instances An object is a self-contained element of a computer program that represents a related group of features and is designed to accomplish specific tasks Objects are also called instances.

Object-Oriented Terminology Object Inheritance Instance Class Behavior Methods State Variables Encapsulation Message Polymorphism Superclass

State and Behavior All real-world objects have state and behavior A software object maintains its state in variables and its behavior in methods.

Instance Variables and Methods Variables and methods associated with a particular object An instance variable is an item of information that defines an attribute or state An instance method is used to implement behavior

Object Diagram Public Interfaces Private Implementation Public Interfaces Details Public Interfaces

Car Object Diagram Change Gears Accelerate 60 mph Overdrive Wipers Off Turn on/off wipers Brake

Encapsulation Hiding information in an object’s center and then providing a public interface for interacting with it is called encapsulation

Benefits of Objects Modularity – source code for an object can be independent from the source code for other objects Information Hiding – private information is kept hidden from the public interface

Messages Rover, Speak! Software objects interact and communicate by sending messages to each other Bark!

Messages With More Meaning change. Gears(reverse) Back Up

Message Components The object to whom the message is addressed The name of the method to perform Any parameters needed

Benefits of Messages Methods – an object’s behavior is expressed through its methods so passing messages supports all possible interaction between objects Location – objects don’t need to be in the same process or even on the same machine to send and receive messages

Classes The most important feature of Object-Oriented Programming Classes embody all features of a set of objects Define classes of objects Software blueprint

Definition of Class A class is a blueprint or prototype that defines the variables and methods common to all objects of certain kind. It is a template used to create multiple objects with similar features

Class Variables and Methods A class variable is an item of information that defines an attribute of an entire class. Class methods implement behavior for the entire class.

Static Variables and Methods Static variables apply to the class itself and to all of its instances Can access static variables and methods from an instance of the class or directly by the class You don’t have to instantiate a class to use its class variables and class methods Static methods only operate on class variables

Benefits of Classes Reusability – programmers can use the same class and therefore the same code over and over again to create different objects

Inheritance Inheritance is the mechanism that enables one class to inherit all of the state and behavior of another class Through inheritance, a class has all the functionality of an existing class A new class can be created by only indicating how it is different from an existing class

Superclass and Subclass A parent-child relationship A class that inherits from another class is a subclass The class that gives the inheritance is the superclass

Car Class Hierarchy Car SUV Mini Van Sports Car

Override Subclasses can override inherited methods and provide specialized implementations for those methods Overriding means to create a different method definition for a method inherited from a subclass Overriding a method can be accomplished by passing a different number of different types of parameters

Benefits of Inheritance Specialized behavior – subclasses provide specialized behaviors from the basis of common variables and methods provided by the superclass Abstract Classes – an abstract class defines generic behavior Reuse – Don’t start code from scratch. Reuse existing classes

Polymorphism By inheriting its superclass’ features, an subclass is still a member of the superclass. It can execute all of it’s methods as well as those of the superclass. This ability to be both a member of subclass and a superclass is called polymorphism. In other words, a sports car is still a car

Comparison to Procedural Languages Object-Oriented Programming � Defines the “what” or the classes first � Then the “how”

Procedure-Oriented Programming First you identify the task to be performed then: 1. 2. Top-Down Approach -- by a step-wise refinement, break the tasks into subtasks Bottom-Up Approach – write procedures to solve simple tasks and combine them into more sophisticated procedures Most Programmers use a mixture of these two approaches

Advantages of Object-Oriented Programming Classes provide a convenient clustering mechanism for methods The Object-Oriented structure is much easier to grasp by the programmer or to handle by teams of programmers Encapsulation – classes hide their data representation from all code except their own classes

Finding a Data-Related Bug Procedural Approach Object-Oriented Approach method function Object Data method function method Global Data method Object Data

Other Differences Modules Single Entity Forced Organization Classes Multiple Entities Natural Organization

Object-Oriented Design Rabbit Class Cat Class Furry Household Pet Class (Abstract) Dog Class

An Object-Oriented Program When we write an Object-Oriented Program, we design and construct a set of classes When the program runs, objects are created from those classes We need to create the right set of classes to accomplish what the program needs to do

Dragon State Color – yellow, red, green Attitude – mean, angry, playful Appetite – full, hungry

Dragon Behavior Get angry Calm down Eat a knight Breath fire

Reasons for Calling Methods To report a change to another object To tell the other object to change something about itself To ask another object to do something

Dragon Scenario Dragon Object � Iam. Dead Instance Method � Numberof. Dragons Class Variable � Reduce. Dragons Class Method Knight Object � Sir Galahad Instance Variable � Chop. Off. Dragon. Head Instance Method

Organizing Classes Determine if classes make up a class hierarchy with subclasses Functionality that is common to multiple classes can be put in superclasses Changes to a superclass are automatically reflected in all their subclases

Monster Class Hierarchy Monster Flying Monster Swimming Monster

Flying Monster Class Hierarchy Flying Monster Four-Legged Flying Monster Mammal Reptile Two-Legged Flying Monster Amphibian

Steps for Object-Oriented Programming Design 1. 2. 3. 4. 5. Break down objects to their smallest features Look for commonality between the objects Look for differences between the objects Find the largest commonality between all objects Put the remaining common objects together and repeat

Break Down Code to its Smallest Features Object Feature Creatures Location, size, power level, capability to attack, maneuverability Power Pieces Must be drawn, location, power level Bullets Capability to be fired Main Character Capability to receive commands from the user, capability to move around the maze according to these commands, capability to attack, location, size

Look For Commonality Between the Objects Look for all the common relationships between each of the objects � The main difference between the creatures and the main character is who controls them � Have main character and creature share code with the exception of the code to move them

Look For Difference Between the Objects Find the differences between each of the objects Look for relationships that unite and separate all of the objects � The bullets move and the power pieces don’t � The computer controls creatures and the user controls the main character

Find the Largest Commonality Between All Objects Draw Object All Game Pieces

Put Remaining Common Objects Together and Repeat Draw Object Creature Main Character Power Pieces/Bullets

The “Big Example” We’re going to take all the Object-Oriented Programming and Object-Oriented Design concepts and ideas and write a Science Fiction Movie entitled… “Programmers In Space”

Space Ship §Has a certain number of space shuttles §Has a certain number of imaging chambers §Has a certain number of officers §Has a certain number of aliens §Is located somewhere §Exists at a certain time A typical Space Ship would have §Number of shuttles = 2 §Location = sigma quadrant §Time period = 2253

Main Plot Space Ship CECS is a new Space Ship §Number of imaging chambers = 1 §Number of officers = 3 §Captain = Danny §Senior Officer = Bob §Senior Officer = Jody §Number of aliens = 5

Humanoids §Have a certain number of legs §Have a certain number of arms §Have a certain number of eyes §Have a certain number of noses §Have a certain number of ears §Have a certain number mouths §Have a name §Have a certain sex §Have a favorite weapon §Have a beverage preference

Humanoids (continued) A Standard Humanoid would start with §Number of legs = 2 §Number of arms = 2 §Number of eyes = 2 §Number of noses =1 §Number of ears =2 §Number mouths = 1 When someone asks for your name §Tell them your name

Aliens extend the idea of Humanoids An Alien §Has non-standard ears §A certain “look” §A prophetic saying §Some level of meanness §A certain quantity of dimodium phosphate tubes For a given Alien §It will look evil §It will start out the day calm §It will not yet have captured any dimodium phosphate tubes

Alien Instance Variables and Methods Drink Beverage §Level of meanness goes up by one How Mean Am I §Tell them how mean I am

Alien Class Variables and Methods Prophetic Saying §Same saying for all aliens of a given species Repeat Prophetic Saying §Retrieve it from the sacred book

Passing Parameters Capture Dimodium Phosphate Tubes (# of tubes) §Increase the quantity of dimodium phosphate tubes by the (# of tubes) amount §Gloat that you have captured (# of tubes) of dimodium phosphate Repeat Prophetic Saying §Retrieve it from the sacred book

Main Routine There is a Space Ship called CECS §Number of imaging chambers = 1 §Number of officers = 3 §Captain = Danny §Senior Officer = Bob §Senior Officer = Jody §Number of aliens = 5 There is a new Human called Jennifer §Jennifer is female §Jennifer favor weapon is a keyboard §Jennifer prefers to drink coffee

Main Routine (continued) There is a new Alien name Bernie §Bernie is male §Bernie has pointy ears §Bernie’s favorite weapon is a test tube §Bernie prefers to drink Pepsi §The prophetic saying spoken by Bernie’s race is “What’s the status of that ticket? ” Bernie drinks some Pepsi Bernie tells Jennifer how mean he is Bernie captures 23 tubes of dimodium phosphate Bernie quotes his prophetic saying

Resources for this Presentation Campione, Mary and Walrath, Kathy. The Java Tutorial Second Edition: Object-Oriented Programming for the Internet. Addison. Wesley. Reading, Massachusetts. 1998. Claerbout, Johannes. Don’t Fear the Oop!. http: //sepwww. standford. edu/sep/josman/oop 1. htm. 1998. Horstmann, Cay and Cornell, Gary. Core Java 2: Volume 1 – Fundamentals. Sun Microsoft Press. Palo Alto, California. 1999. Lemay, Laura and Cadenhead, Rogers. Teach Yourself Java 2 in 21 Days. Sams Publishing. Indianapolis, Indiana. 1999. Weber, Joseph L. Special Edition: Using Java 2 Platform. Que Publishers. 1999.