OBJECT ORIENTED PROGRAMMING

Transcription

1 OBJECT ORIENTED PROGRAMMING Course 1 Loredana STANCIU Associate Professor at Automation and Applied Informatics Department of Automation and Computer Science Faculty loredana.stanciu@upt.ro Room B616

2 About the course Every week: 3 hours of course Monday, 11:00-14:00 room A316 3 practical activities: Thursday 8:00-14:00, room B613

3 The examination Distributed evaluation several marks 2 written examinations (multiple choice written tests) you have the possibility to improve your marks at written tests the average of these two marks = 2/3 of the final mark 2 practical tests the mark from one practical test can be also improved the average of these two marks = 1/3 of the final mark

4 SCHEDULER W 1 W 2 W 3 W 4 W 5 W 6 W 7 W 8 W 9 W 1 0 W 1 1 W 1 2 W 1 3 W 1 4 C o u r s e C C C C C E1 P1 C E1 P2 C C C E2 P1 E2 P2 L a b L1 H W L2 CO L3 IOS L4 I&P L5 I L6 Ex L7 E L8 T1 L9 C L10 G L11 G L12 G L13 T2 R

5 A survey of programming techniques Unstructured programming

6 Unstructured programming Small and simple programs consisting only of one main program A sequence of commands or statements which modify data (global) throughout the whole program

7 Unstructured programming #include <stdio.h> #include <conio.h> void main(void){ int a; clrscr(); printf( a= ");scanf( %d,&a); printf( a= %d,a); }

8 Unstructured programming Disadvantage: large programs using the same statement sequences Idea Extract these sequences, name them and offer a technique to call and return from these procedures

9 A survey of programming techniques Unstructured programming Procedural programming

10 Procedural programming Combines returning sequences of statements into one single place A procedure call is used to invoke the procedure With parameters and subprocedures programs can now be written more structured and error free

11 Procedural programming #include <stdio.h> #include <conio.h> int add(int a, int b){ return a+b;} void main(void){ int a,b,c; clrscr(); printf( a= ");scanf( %d,&a); printf( b= ");scanf( %d,&b); c=add(a,b); printf( c= %d,c); }

12 Procedural programming A single program divided into small pieces called procedures Enable usage of general procedures or groups of procedures in other programs, they must be separately available

13 A survey of programming techniques Unstructured programming Procedural programming Modular programming

14 Modular programming Procedures of a common functionality are grouped together into separate modules A program is now divided into several smaller parts which interact through procedure calls and which form the whole program

15 Example handling single lists Programs use data structures to store data Characterized by their structure and their access methods To program a list in a modular programming language: the interface definition the implementation file

16 Example handling single lists /* * Interface definition for a module which implements * a singly linked list for storing data of any type. */ MODULE Singly-Linked-List-1 BOOL list_initialize(); BOOL list_append(any data); BOOL list_delete(); list_end(); ANY list_getfirst(); ANY list_getnext(); BOOL list_isempty(); END Singly-Linked-List-1 Hiding information

17 Example handling Multiple lists /* * A list module for more than one list. */ MODULE Singly-Linked-List-2 DECLARE TYPE list_handle_t; list_handle_t list_create(); list_destroy(list_handle_t this); BOOL list_append(list_handle_t this, ANY data); ANY list_getfirst(list_handle_t this); ANY list_getnext(list_handle_t this); BOOL list_isempty(list_handle_t this); END Singly-Linked-List-2; List objects

18 Modular programming problems 1) Explicit Creation and Destruction PROCEDURE exp() BEGIN list_handle_t mylist; int x; mylist <- list_create(); /* Do something with mylist */ x=3;... list_destroy(mylist); END

19 Modular programming problems 2) Decoupled Data and Operations A structure based on the operations rather than the data defined operations specify the data to be used In object-orientation, structure is organized by the data modules group data representations together

20 Modular programming problems 3) Missing Type Safety PROCEDURE exp() BEGIN SomeDataType data1; SomeOtherType data2; list_handle_t mylist; mylist <- list_create(); list_append(mylist, data1); list_append(mylist, data2); /* Oops */... list_destroy(mylist); END

21 Modular programming problems The compiler cannot guarantee for type safety a mechanism which allows to specify on which data type the list should be defined list_handle_t<apple> list1; /* a list of apples */ list_handle_t<car> list2; /* a list of cars */

22 Modular programming problems 4) Strategies and Representation A cursor is used to point to the current element a traversing strategy which defines the order in which the elements of the data structure are to be visited Separate the actual representation or shape of the data structure from its traversing strategy

23 A survey of programming techniques Unstructured programming Procedural programming Modular programming Object-oriented programming

24 Object Oriented Programming Solves some of the mentioned problems A web of interacting objects, each housekeeping its own state

25 Object Oriented Programming Each object implements its own module allowing for example many lists to coexist Each object is responsible to initialize and destroy itself correctly Some authors describe object-oriented programming as programming abstract data types and their relationships Real-life problems are nebulous and the first thing you have to do is to try to understand the problem

26 Object Oriented Programming HANDLING PROBLEMS Abstraction : It is an act of representing only the essential things without including background details Focuses on what not how Similar with a table of content Necessary for managing large, complex software projects

27 Object Oriented Programming HANDLING PROBLEMS Define properties of the problem: the data which are affected and the operations which are identified An example: the administration of employees in an institution: name, date of birth, shape, social number, room number, hair color, hobbies problem specific properties the abstract employees data operations

28 Object Oriented Programming

29 Object Oriented Programming PROPERTIES OF ABSTRACT DATA TYPES With abstraction one can create a well-defined entity: Define the data structure of a set of items The data structure can only be accessed with defined operations interface exported by the entity abstract data type (ADT)

30 Object Oriented Programming PROPERTIES OF ABSTRACT DATA TYPES 1) It exports a type 2) It exports a set of operations. This set is called interface 3) Operations of the interface are the one and only access mechanism to the type's data structure 4) Axioms and preconditions define the application domain of the type

31 Object Oriented Programming IMPORTANCE OF DATA STRUCTURE ENCAPSULATION Encapsulation: The principle of hiding the used data structure and to only provide a well-defined interface The separation of data structures and operations and the constraint to only access the data structure via a well-defined interface allows you to choose data structures appropriate for the application environment Encapsulation: Wrapping up of data and methods into a single unit Information Hiding: It is a concept that can be use for hiding data from external world. And that can be achieved using Encapsulation and Abstraction.

32 Object Oriented Programming EXAMPLE OF DATA STRUCTURE ENCAPSULATION Define an ADT for complex numbers Structure (real part and imaginary part) Operations (addition, subtraction, multiplication or division) Two ways of representing: An array: x=c[0], y=c[1] Two-valued record: x=c.x, y=c.y

33 Object Oriented Programming IMPLEMENTATION OF ABSTRACT DATA TYPES A class: an actual representation of an Abstract Data Type provides implementation details for the data structure used and operations class Integer { attributes: int i methods: setvalue(int n) Integer addvalue(integer j) } Definition (Class) A class is the implementation of an abstract data type (ADT). It defines attributes and methods which implement the data structure and operations of the ADT, respectively.

34 Object Oriented Programming An object: uniquely identifiable by a name the set of values at a particular time is the state of the object Definition (Object) An object is an instance of a class. It can be uniquely identified by its name and it defines a state which is represented by the values of its attributes at a particular time Definition (Behaviour) The behaviour of an object is defined by the set of methods which can be applied on it.

35 Object Oriented Programming

36 Object Oriented Programming A running program is a pool of objects where objects are created, destroyed and interacting through messages Integer i; /* Define a new integer object */ i.setvalue(1); /* Set its value to 1 */ Definition (Message) A message is a request to an object to invoke one of its methods. A message therefore contains: the name of the method and the arguments of the method. Definition (Method) A method is associated with a class. An object invokes a method as a reaction to receipt of a message.

37 Object Oriented Programming A program with interacting objects

38 Object Oriented Programming Problem: how a character appears on the screen when you type a key Procedural programming 1. wait, until a key is pressed. 2. get key value 3. write key value at current cursor position 4. advance cursor position Object oriented programming 1) the key receive a message to change its state to be pressed 2) its corresponding object sends a message to the screen object. 3) the screen object receive the message to display the associated key value

39 Object Oriented Programming Write a drawing program Various objects such as points, circles, rectangles, triangles and many more class Point { attributes: int x, y methods: setx(int newx) getx() sety(int newy) gety() } class Circle { attributes: int x, y, radius methods: setx(int newx) getx() sety(int newy) gety() setradius(int newy) getradius() }

40 Object Oriented Programming Relationships Between two similar classes A-Kind-Of relationship Between objects of classes in A-Kind-Of relationship Is-A relationship

41 Object Oriented Programming Build objects by combining them out of others class Logo { attributes: Circle circle Triangle triangle methods: set(point where) } Relationships: Part-Of relationship

42 Object Oriented Programming Inheritance able to make use of the a-kind-of and is-a relationship when the classes share properties class Circle inherits from Point { } attributes: int radius methods: setradius(int newradius) getradius() Circle acircle acircle.setx(1) /* Inherited from Point */ acircle.sety(2) acircle.setradius(3) /* Added by Circle */

43 Object Oriented Programming Definition (Inheritance) Inheritance is the mechanism which allows a class A to inherit properties of a class B. We say A inherits from B. Objects of class A thus have access to attributes and methods of class B without the need to redefine them. Definition (Superclass/Subclass) If class A inherits from class B, then B is called superclass of A. A is called subclass of B Superclasses are also called parent classes Subclasses may also be called child classes or just derived classes

44 Object Oriented Programming Static Binding In strongly typed programming languages you have to declare variables prior to their use int x, y float z x= a /* type mismatch Definition (Static Binding) If the type T of a variable is explicitly associated with its name N by declaration, we say, that N is statically bound to T. The association process is called static binding.

45 Object Oriented Programming Dynamic Binding Some languages allow to introduce variables once they are needed Definition (Dynamic Binding) If the type T of a variable with name N is implicitly associated by its content, we say, that N is dynamically bound to T. The association process is called dynamic binding

46 Object Oriented Programming Packaging Collections of classes and interfaces that are related to each other in some useful way Benefits: The ability to organize many class definitions into a single unit. The "friendly" instance variables and methods are available to all classes within the same package, but not to classes defined outside the package

47 Summary A fundamental principle in object oriented programming to view a program as a collection of interacting objects Objects in a collection: react upon receipt of messages, change their state according to invocation of methods which might cause other messages sent to other objects

48 What is java? Late 1980s C++ was widely used to write OOP: not a platform independent needed to be recompiled for each different CPUs 1991 a team of Sun Microsystems makes a platform independent software and named it Oak 1995 Java

49 What is java? Java influenced by C, C++, Smalltalk slogan named Write Once Run Anywhere it can develop and run on any device equipped with Java Virtual Machine (JVM). applicable in all kinds of operating systems associated with the World Wide Web a platform independent programming language can be found in a variety of devices like cell phones, e-commerce application, PCs and almost all network or computing devices

50 Why Java? 97% of Enterprise Desktops Run Java 89% of Desktops (or Computers) in the U.S. Run Java 9 Million Java Developers Worldwide #1 Choice for Developers #1 Development Platform 3 Billion Mobile Phones Run Java

51 Why Java? 100% of Blu-ray Disc Players Ship with Java 5 Billion Java Cards in Use 125 million TV devices run Java 5 of the Top 5 Original Equipment Manufacturers Ship Java ME

52 Why developers choose Java? Write software on one platform and run it on virtually any other platform Create programs that can run within a web browser and access available web services Develop server-side applications for online forums, stores, polls, HTML forms processing, and more

53 Why developers choose Java? Combine applications or services using the Java language to create highly customized applications or services Write powerful and efficient applications for mobile phones, remote processors, microcontrollers, wireless modules, sensors, gateways, consumer products, and practically any other electronic device

54 The java language All source code written in plain text files ending with the.java extension. Source files compiled into.class files by the javac compiler..class file contains bytecodes the machine language of the Java Virtual Machine. java launcher tool then runs your application with an instance of the Java Virtual Machine.

55 The java language Java VM available on many different operating systems, the same.class files are capable of running on Microsoft Windows, the Solaris TM Operating System (Solaris OS), Linux, or Mac OS

56 The java language

57 The java platform A platform the hardware or software environment in which a program runs. Java a software-only platform that runs on top of other hardware-based platforms: The Java Virtual Machine The Java Application Programming Interface (API) a large collection of ready-made software components that provide many useful capabilities grouped in packages

58 Java characteristics Simple, Object Oriented, and Familiar: Simple language, easy to learn Provides a clean and efficient object-based development platform Keeping the Java programming language looking like C++ as far as possible results in it being a familiar language

59 Java characteristics Robust and Secure Designed for creating highly reliable software The memory management model is extremely simple: objects are created with a new operator The system will find many errors quickly Security features designed into the language and runtime system Java technology constructs applications that can't be invaded from outside

60 Java characteristics Architecture Neutral and Portable The Java Compiler TM product generates bytecodes--an architecture neutral intermediate format designed to transport code efficiently to multiple hardware and software platforms Programs are the same on every platform. There are no data type incompatibilities across hardware and software architectures

61 Java characteristics High Performance The interpreter can run at full speed without needing to check the run-time environment The automatic garbage collector runs as a low-priority background thread

62 Java characteristics Interpreted, Threaded, and Dynamic The Java interpreter can execute Java bytecodes directly on any machine to which the interpreter and runtime system have been ported Java technology's multithreading capability provides the means to build applications with many concurrent threads of activity (results in a high degree of interactivity for the end user) The language and run-time system are dynamic in their linking stages

63 References Peter Muller, Introduction to Object-Oriented Programming Using C++, Chapters 1, 2, 3 and 4, ml The Java Tutorials. Getting Started. /index.html