Object-Oriented Programming Overview

Object-Oriented Programming (OOP) Overview

• OOP is a programming paradigm that combines data and functions into a single unit called an object.
• This contrasts with structured programming where data and functions are separate.

Books Mentioned

• Intro to Java Programming, Comprehensive Version, 10th Edition, by Y. Daniel Liang (2015), published by Prentice Hall.
• An Introduction to Object-Oriented Programming with Java, 5th Edition (2009).

Structured Programming

• A program in a procedural language is a list of instructions.
• A procedural program is divided into functions.
• Each function has a defined purpose and a defined interface to other functions.
• Dividing a program into functions is called structured programming.

Disadvantages of Structured Programming

• Large programs become overly complex.
• There's no data protection, allowing unrestricted access to global data by functions.
• Changing a single global data item may require modifying all functions that access it, making large programs difficult to modify.
• It's a poor model of the real world where functions and data aren't related.
• Real-world objects have both attributes and behaviors.

Object Attributes and Behavior

• Attributes (or characteristics) of real-world objects are equivalent to data in programs.
• Attributes are specific values like name, eye color, height, car color, horsepower, or number of doors.
• Behavior is what an object does in response to a stimulus like applying brakes in a car.
• Behavior is similar to a function to accomplish something.

Object-Oriented Languages

• The fundamental concept behind object-oriented languages is to combine data and functions that operate on that data into a single unit, called an object.

Objects

• An object consists of member data and a group of member functions.
• Objects' member functions provide the only way to access their member data.
• To read data, call a member function in the object; it accesses the data and returns the value.
• Direct access to object data isn't possible; data is hidden within the object.

OOP Characteristics

• Data and its functions are encapsulated into a single entity
• Data encapsulation and data hiding are key terms in Object-Oriented Programming (OOP).
• Modifying data involves calling an object's member function, which interacts only with that data.
• This simplifies the writing and modification of large and complex programs.

Object Communication

• Programs typically consist of numerous objects.
• Objects communicate with each other by calling each other's member functions.
• This communication is called sending messages.

Inheritance

• The vehicle class, for example, gets divided into cars, trucks, buses, motorcycles, etc.
• This division's principle is that each subcategory (subclass) shares features with the main category (class) from which it derives.
• Subcategories (e.g., types of vehicles) share common features (e.g., wheels, motor) from the parent category (vehicles).
• Each subclass also has unique characteristics. For instance, buses have many seats while trucks have hauling space.
• The original class is called the base class; derived classes share characteristics and further attributes.

Polymorphism

• OOP enables defining new behaviours for known operators (+, -, *). This is operator overloading.
• These operations are member functions of a specific class.
• Calling the overloaded operators essentially calls a specific member function within the class.
• Operator overloading is a type of polymorphism.

Popular Object-Oriented Programming Languages

• C++
• Java
• Smalltalk
• Eiffel
• Ruby
• Delphi

Characteristics of OOP

• Programs are divided into classes and functions.
• Data is hidden within an object and is not externally accessible.
• Inheritance facilitates the reuse of code.
• Adding new functions and data items is straightforward.
• Data holds more significance than functions.
• Data and functions are joined in a single unit called a class.
• Objects communicate by sending messages (in the form of functions).

Advantages of OOP

• Code reusability through inheritance.
• Complex projects divided into smaller functions.
• Abstraction and encapsulation lead to secure program development.
• Reduced software complexity.
• Data hiding enhances program safety.
• Enables rapid software development.
• Multiple instances of the same class can exist simultaneously without interference.

Introduction to Objects

• An object embodies something in a program with which interaction is possible.
• An object comprises member data and methods.
• Objects provide services that allow instructions for tasks to be performed.
• Classes define the services of objects.
• A class represents a concept, and an object is an instance of a class. Classes enable the creation of numerous objects.

Classes vs. Objects

• Classes represent conceptual models.
• Objects are real-world implementations embodying class characteristics.
• Multiple objects can be generated from a single class.

Class vs. Object

• A class is a blueprint or pattern for creating objects.
• Defining a class does not generate an object. This is comparable to creating a data type (int, float) - it doesn't automatically populate variables of these types.
• An object is an instance of a class (a specific example from the class' blueprint).
• A single class can be used to form numerous objects.

Classes (in Detail)

• Classes are new types of variables.
• Class definition specifies needed data and possible actions.
• Method is an object-oriented equivalent of a function.

Using Objects

• System.out object acts as output destination for instructions.
• Methods (e.g. println) are invoked on the object to execute actions.

Attributes of a Class

• Attributes, or variables, hold characteristics of a class' instances (objects).
• Attributes can be either variable or constant (constant preceded by "final").
• Each object shares the attribute definition but has a unique value for it.
• An object's attributes' current values are what determine its state.

Methods

• Methods represent actions or behaviors of class instances.

Methods of a Class

• Methods have specific formats for return types, access modifiers, and parameters.

Object Instantiation

• An object's instantiation creates or prepares a new object (a particular realization of a class blueprint).
• Instances of classes are objects.
• The format includes the class name, instance name, and instantiation keyword ('new').

Constructor

• A special method used to initialize an object's attributes upon creation/instantiation.

Default Constructor

• A constructor, if not defined, is automatically created and implicit within the Java language.

Calling Methods (Outside the Class)

• Calling a method requires prefacing the method with a class variable (which represents a reference to an object of that class)

Calling Methods (Inside the Class)

• Calling methods within a class directly refers to the method name.

Example (Code Snippet)

• Example code (showing object instantiation, class definition, method calls)

Private Keyword

• private keyword syntactically specifies that class members aren't accessible outside the class.
• The private keyword is most often used for attributes (data members).

Encapsulation

• Encapsulation (information hiding) hides internal data; only defined methods may access private data members.
• Public methods can then access this private data via methods.
• This way, private data is protected from external modification.
• It also leads to preventing invalid states.

Assignment 1 (Problems)

• Write a program printing "Hello world"
• Write a program printing name, address, phone number.
• Create a rectangle class
  • data members (length, height),
  • methods to enter attributes, display them, compute area and perimeter and default constructor (initializing attributes to zero)