Object Oriented Programming. Michał Bereta

Transcription

1 Object Oriented Programming Michał Bereta

2 Time and place Thursday, 18:00 20:15 Classroom 142 Institute of Informatics Warszawska street (Faculty of chemistry building)

3 Scope Procedural vs. Object Oriented approaches What is OO approach? Classes and interfaces in detail Modeling with UML Design Patterns Projects and programming

4 Scope Languages (? to be discussed) Java C# C++ Tools (programming) NetBeans Eclipse Visual Studio (free Express edition available) Tools (modelling) StarUML ArgoUML Visual Paradigm for UML Community Edition (VP-UML CE) Eclipse Model Development Tools (MDT)

5 Books Thinking in Java, 4th edition, Bruce Eckel Object-Oriented Thought Process, The (3rd Edition), Matt Weisfeld Design Patterns: Elements of Reusable Object- Oriented Software, Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides Head First Design Patterns, Elisabeth Freeman, Eric Freeman, Bert Bates, Kathy Sierra, Elisabeth Robson

6 Books

7 Procedural versus OO Programming Procedural programming Attributes and behaviours are normally separated. OO programming Attributes and behaviours are contained in single object.

8 Procedual programming C-like example

9 Procedual programming What is wrong with procedural programming? Nothing, if it is done correctly and carefully, but hard to control data access there is often global data hard to test and debug OO programming: reflects better the real world and the way people perceive it is better for problem modelling is more flexible and allows for programming techniques not easy or impossible in procedural programming

10 Most popular programming paradigm but it is not the case of object oriented databases In OO model: Data attributes Behaviour methods Object = attributes + behaviours Class: a description of objects of a certain type, a blueprint for and object of a given type Objects are defined by classes and classes are explained in terms of objects However, when programming you need to define a class first, then you can create objects

11 Data integrity: when properly designed there is no global data in OO design In OO design objects communicate with each another by sending requests/messages and answering them

12 Encapsulation Data and implementation hiding Creating public interfaces Inheritance Abstraction Generalization Specialization Single-inheritance Multiple-inheritance Polymorphism Composition Aggregation Association

13 Encapsulation combining attributes and methods in the same entity (object) Data hiding restricting access to certain attributes and / or methods Make attributes and methods as much private as possible Use public getter and setter methods for attributes when needed Public interface should be as limited as possible

14 Interface The public part of an object Allows other objects to communicate with a given object Interface = public attributes + public methods Separate the public interface from the concrete implementation It allows to introduce changes into the implementation There is no need to change the code of all the users of this class (they communicate only by the public interface)

15 Inheritance Allows a class to inherit the attributes and methods of another class Allows creation of new classes by abstracting out common attributes and behaviours

16 Inheritance Super class (parent class) contains attributes and behaviours that are common to all classes that inherit from it. Child classes

17 Inheritance This is not multiple inheritance! Java and C# do not allow a class to have multiple parents. However, a class may have multiple children. Multiple inheritance is possible e.g. in C++

18 Abstraction Process of creation of the inheritance tree Single-inheritance (Java, C#) A class can extend only one class A class may implement many interfaces Multiple-inheritance (C++) A class may extend multiple classes The are no interfaces in C++ (however, the same effect can be achieved by abstract classes

19 Abstraction Can be done as Generalization Take several classes and check what is the common part of all of them Example: Take Dog and Cat and create class Animal Specialization Take existing class and create classes with more specific/detailed/modified attributes/behaviours Example: Having class Animal create classes Dog and Cat

20 Inheritance Inheritance is is-a relation between objects Example: Dog is-a Animal

21 Polymorphism Greek word, means many shapes Most powerful advantage of OO technologies Each object responds to the messages in its own way, although the interface is inherited from the parent class and is common for all child classes Example: Animals make noises. When you take a Dog ( is-an Animal) and ask it to make a noise it will know it should bark

22 Composition Objects may contain other objects It is has-a relationship Example: Car has-a SteeringWheel (we cannot say neither Car is-a SteeringWheel nor SteeringWheel is-a Car)

23 Composition Aggregation Association

24 Composition Aggregation Complex object composed of other objects.

25 Composition Association One object wants other object to perform a service for it. Example: Stereo set consists of several parts (CD player, Tuner, Speakers, etc.) which cooperate to perform the task (are associated with each another)