OOP Collaboration Chapter 4 Quiz

Chapter 4: Collaboration between classes and methods (Part 1)

• Dr. Sarra Namane, Department of Computer Science, Djibou Mokhtar University, Annaba Class, 2nd Year Engineering, Year: 2024/2025.

Introduction

• Object-Oriented Programming (OOP) focuses on how objects interact to create effective software systems.
• The course covers key concepts including message passing, class association, class dependency, and chain reaction messaging.

Message Passing

• Objects communicate by sending and receiving data, or invoking methods.
• Example: A coffee machine (Object A) tells a cup (object B) to fill with coffee by calling the fillCup() method.

Message Passing (2)

• One object sends a message to another object by calling a method.
• Example code provided in Java.

Class Association

• Class association shows the relationships between different classes.
• Example: A Teacher class (Class A) knows about a Student class (Class B) to assign homework.

Class Association (2)

• The Teacher class has a reference to a Student object.
• This allows the Teacher to call the doHomework() method on the Student object.
• Example code in Java.

Class Association (Reference)

• Classes communicate through reference attributes.
• One class can include a reference to another class.
• Example: A Library class can store information about books in its book attribute.

Class Association (Reference) (2)

• Example code in Java for a Library class and a Book class where the library references the book.

Class Association (Reference) (3)

• The library class references the book class to access its details.
• The relationship is not reciprocal.
• Example: The Library class holds a reference to the book class.

Class Association (Reference) (4)

• The library is responsible for managing the books.
• The book doesn't need to know about the library.

Class Association (Reference) (5)

• The library manages the books.
• The book is part of the library's collection, but doesn't manage the library.
• The library can have methods to add and remove books.

Class Dependency

• A class temporarily depends on another class during a specific method execution.
• Example: A car class depends on an engine class to start. This dependency only exists during the startCar method.

Class Dependency (2)

• Example code in Java for Car and Engine classes.

Class Dependency (3)

• The car needs the engine to start, but does not keep a permanent reference to it.
• The interaction between the classes is temporary and only exists during the method call.

Class Dependency (4)

• A Printer class interacts with a Document class while printing.
• The interaction ends once the printing process is complete.
• Example code in Java demonstrating class dependency.

Class Dependency (5)

• Class dependency is where one class uses another class for a short-lived task, which ends when the method finishes executing..
• Example: Car class and the Engine class; a Printer class and a Document class

Chain Reaction of Messages

• A chain reaction occurs when one object sends a message to another, that triggers another and so on.
• Example: Customer support request involving multiple steps (SupportAgent, IssueTracker, Database)

Chain Reaction of Messages (2)

• Example code in Java for a customer support system that demonstrates communication between objects
• IssueTracker sends a message to Database
• SupportAgent sends a message to IssueTracker

Chain Reaction of Messages (3)

• The customer support process can be viewed as a sequence of message passing.
• The customer sends a request, which the SupportAgent handles.
• It requires checking with IssueTracker
• The issue is logged and update Database

QCM (Multiple Choice Questions)

• Various questions on the fundamentals of object-oriented programming concepts.
• Answers to the QCM are not provided in these notes.

Ending the Conflict Between Classes

• Classes are responsible for their own data.
• One class doesn't directly modify another class's data.
• Example: A BankAccount class manages its own balance.

Ending the Conflict Between Classes (2)

• Objects of different classes communicate via method calls.
• The process is known as message passing.
• The class to which the message is sent handles the appropriate method to deal with the message.

Java Compilation and Class Linking

• In Java, each class is stored in its own file, e.g., ClassA.java..
• Compiling one source file can automatically compile necessary dependent classes.

One Class, One File

• Java enforces separation of classes into separate files.
• This facilitates class organization within a project.

Unidirectional vs. Bidirectional Associations

• Unidirectional: One class knows about the other but not vice-versa.
• Bidirectional: Both classes know about each other.
• Example code illustrates each case.

Passing Arguments by Value in Java

• In Java, objects are primarily passed by reference.
• A method receives a copy of the reference to the object, not a copy of the object itself.
• Modifying the object within the method affects the original object.

Passing Arguments by Value in Java (2)

• Java code example demonstrating the pass-by-value method with the 'pages' variable.

Passing Arguments by Value in Java (3)

• Java code example demonstrating the 'totalPages' variable passed to the 'printPages' method is modified, but the original variable remains unchanged

Passing Arguments by Value in Java (4)

• This process ensures that only the local copy of the argument is modified in the method.

Passing Arguments by Value in Java (5)

• Java creates a temporary copy of the argument—any changes made to the local copy do not affect the original variable.

Passing an object as an argument in Java

• Objects are passed to methods by reference.
• Changes to the passed object will alter the original object.
• Example code in Java provided illustrating the process.

Passing an object as an argument in Java (3)

• Passing "myCar" object as an argument in Java code.
• Demonstrates interaction between Car and FuelStation classes.

Passing an Object as an Argument in Java (5)

• A copy of the reference is passed.
• The method modifies the actual object—a significant difference from passing simple values.

Passing arguments by reference in Java

• In object-oriented programming, methods often operate on a reference, not a copy of the object.
• Example in Java with a Book and Library illustrating the behavior

Passing arguments by reference in Java (3)

• Example Java code demonstrating a method receiving a Book object by reference.

Is Every Method a Message?

• A method call is not necessarily the same as a message.
• A message only depends on the signatures (name, parameters, and return type) of the method.

Is Every Method a Message? (2)

• The Person object calls car.start() without needing to know the internal mechanism of the 'start' method.

Same Message, Multiple Methods (Polymorphism)

• Polymorphism allows multiple implementations of the same method signature.
• Example code in Java with animal classes illustrating polymorphism.

Same Message, Multiple Methods (Polymorphism) (2)

• Example code in Java with the Animal, Dog, and Cat classes to demonstrate polymorphism.

Same Message, Multiple Methods (Polymorphism) (3)

• Polymorphism ensures different objects respond to the same message in unique ways..
• The message's method signature doesn't require knowing implementation.

Interface and Encapsulation

• The interface defines the methods that can be accessed from outside.
• Encapsulation protects internal workings.
• Objects communicate solely via interface methods.

Interface: List of Available Method Signatures

• Interface focuses on the methods accessible from outside.
• Objects communicate without needing the internal implementation details.
• Private methods or member variables aren't visible to other objects.

Strictly Private Methods

• Private methods are intentionally not exposed in the interface.
• They serve internal purposes within the class.
• Example: Car gears and accelerator, or file saving.

Globalization of Messages

• Messages in OOP can traverse entire computer networks via internet.
• Messages rely on specific object addresses and interfaces to ensure successful communication between unrelated objects.

Globalization of Messages (2)

• Objects communicate using internet addresses..
• The first object must know the services interface to send messages correctly.

Globalization of Messages (3)

• Distributed object methods, such as Java-RMI, CORBA, or web services, streamline the process of communicating through the internet.
• By standardizing object addresses and activation strategies, distributed application development becomes similar to local application.

Distributed Computing

• System applications are spread across various computers.
• This involves delegating tasks from one computer to another.
• The idea of distributed computing leverages object-oriented programming design.

QCM (2)

• Multiple choice questions (and answers) about the concepts of OOP.

Test your understanding of collaboration between classes and methods in Object-Oriented Programming. This quiz covers key concepts such as message passing, class association, and dependencies, focusing on their roles in effective software systems. Dive into practical examples and strengthen your knowledge in OOP.