Object-Oriented Programming Concepts

Chapter 2: Classes and Objects

• The chapter covers classes and objects in Java programming.
• The lecturer is Dr. Sarra Namane from the Department of Computer Science, Adj Mokhtar University, Annaba.
• The target audience is 2nd-year engineering students in the 2024/2025 academic year.

Constituting a Class of Objects

• Object-oriented programming (OOP) primarily focuses on classes.
• Classes define the structure and behavior of objects.
• Objects are instances of classes.
• Objects use data structures that link attributes to methods to access them.
• Every object follows the rules defined by its class.
• Object roles can change in real life but not in object-oriented programming.
• OOP restricts objects to their class.

The Three Constituent Parts of a Class

• Every class has a name.
• Attributes define the data associated with a class.
• Methods define the behavior of a class.
• Example: A Car class has attributes like make, model, and year and methods like start() and stop().

Definition of a Class Method: With or Without Return

• A method can return a value or perform an action.
• Methods can take arguments, used in processing.
• Example: A Rectangle class has a calculateArea() method returns the area.

Comments

• Comments are used to explain code, ignored by the compiler.
• // for single-line comments.
• /* */ for multi-line comments.
• Comments are important to explain complex code.

Functions and Procedures

• Functions in procedural programming return a value.
• Procedures in procedural programming do not return a value.
• Methods in OOP can accept arguments (input data).
• Example: printProduct method that prints the product of two numbers but does not return a value.

Identification and Overloading of Methods by Their Signature

• A method's signature consists of its name and the data type of its arguments.
• Matching signatures ensure unique method instructions.
• Overloading: same method name, different argument lists.
• Example: add method can add integers or decimals.

Identification and Overloading of Methods by Their Signature (2)

• Overloading enables methods with the same name but different arguments to exist within a class.
• Overloading adds flexibility through providing diverse behavior within the same class for differing data types.
• It's important that overloaded methods provide different signatures, this is how the compiler can distinguish which method to use.

The Class as a Functional Module: Differentiating Objects by Attribute Values

• Classes define the structure and behavior of objects, simplifying management of large sets of objects.
• This helps manage many objects of similar types, such as cars.
• Objects stored in collections (lists or arrays).
• Differentiation of objects within the same class relies on different attribute values.

The Constructor

• A constructor is a special method used to create objects and initialize their attributes.
• It has the same name as the class.
• It does not have a return type.
• It's automatically executed when creating an object.
• It's recommended to define your constructor to handle attribute initialization, even if the default is provided.
• Constructors are often overloaded to meet different initialization needs and types.

The Default Constructor

• The default constructor is a no-argument constructor.
• The compiler automatically provides this if no constructors are defined.
• The default constructor sets object attributes to default values, like null for objects and 0 for numbers.
• If you create your own constructor(s), the default constructor is not provided. Note: the default values do not need user-created code for this.

Different Constructors

• A class can have multiple constructors with different parameters, enabling diverse object initialization.
• Using different arguments for constructor calls will create objects initialized with specified parameters.

The Class as a Guarantee of Proper Use

• Classes play a role in program reliability and consistency.
• Compilers, in strongly typed languages (e.g., Java, C++, C#), verify that objects are used safely, preventing unexpected execution behavior.
• Scripted languages (e.g., Python, PHP) have less rigorous checking, making them more flexible but potentially prone to errors during execution.
• Compilation vs execution: Compilation is required for strong typing while, scripting languages are faster but compilation is not needed, making them potentially faster to develop.
• The class is important for program organization, reliability, and consistency.

Strongly Typed Languages

• Languages like Java, C++, and C# are strongly typed.
• Strongly typed languages require the type of variables to be declared when creating the variable.
• The compiler ensures that variables are only used in ways consistent with their declared types.

Dynamic Memory vs. Static Memory

• Static vs dynamic memory: Static is allocated at compile time and not modified during runtime. Dynamic is allocated and deallocated during runtime.
• Stack Memory (static): a memory space using a last-in, first-out methodology.
• Dynamic Memory: allocated and deallocated at runtime. new keyword introduces dynamic memory, used to create and allocate needed memory. Note the need for explicit address management in languages that use pointers.

Static

• Static attributes of a class are shared among all objects of that class.
• Methods that operate on these static attributes or are related to the class use static.
• Static attributes and methods are accessed directly through the class's name.

Class Methods vs. Instance Methods

• Instance methods operate on specific objects.
• Static methods operate on the class, not a specific object.
• Example: main() method is static and used by the JVM to start the program.

Classes, Files, and Directories

• Related classes are grouped into packages.
• Files are grouped within directories that correspond to the packages.

Natural and Dynamic Linking of Classes

• Natural: The method calls between classes are simple.
• Dynamic: In Java, the compiler links classes during compilation and execution. The Java runtime links the needed classes at run time.

Learning Exercise (Questions and Answers)

• These are a series of questions that help learners deepen their understanding of classes and objects.
• Answers to the questions can provide more detailed information to further clarify the concepts.

Test your knowledge of object-oriented programming concepts with this quiz. Explore class definitions, methods, attributes, and the roles of objects. Challenge yourself on core principles that define how OOP operates in programming languages like Java.