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Complete Object Oriented Programming in Short

1. Object Oriented Thinking vs Procedural Programming

  • Procedural Programming:
    • Focuses on breaking down a problem into step-by-step procedures or functions.
    • Data and functions are separate entities.
    • Well suited for smaller, less complex problems.
  • Object Oriented Programming (OOP):
    • Inspired by real-world objects and their interactions.
    • Combines data (attributes) and functions (methods) into self-contained units called objects.
    • Objects interact with each other to achieve a goal.
    • More modular, reusable, and maintainable for complex systems.

2. Features of Object Oriented Paradigm

  • Objects: Represent real-world entities with data (attributes) and functionalities (methods).
  • Classes: Blueprints for creating objects, define attributes and methods.
  • Inheritance: Allows creating new classes (subclasses) that inherit properties and functionalities from existing classes (superclasses).
  • Encapsulation: Bundles data and methods together, restricting direct access to internal data, promoting data integrity.
  • Polymorphism: Ability for objects of different classes to respond differently to the same message (method call).

3. Merits and Demerits of OO Methodology


  • Modular Design: Encourages code reusability and maintainability.
  • Data Hiding: Protects data integrity and reduces complexity.
  • Flexibility: Inheritance allows for code extension.
  • Real-World Modeling: Easier to understand complex systems.


  • Steeper Learning Curve: Concepts like inheritance and polymorphism can be initially challenging.
  • Overhead: Creating and managing objects can add complexity for simple tasks.
  • Overuse: Not every problem requires an object-oriented solution.

4. Object Model

  • A representation of a system using objects and their relationships.
  • Helps visualize the interactions between different parts of the system.

5. Elements of OOPs

  • Classes: Templates for creating objects.
  • Objects: Instances of classes with specific attributes and behaviors.
  • Attributes: Data properties of objects.
  • Methods: Functions defined within objects that operate on their data.
  • Inheritance: Mechanism for creating new classes from existing ones.
  • Polymorphism: Ability of objects to respond differently to the same message.
  • Encapsulation: Bundling data and methods together.
  • Abstraction: Hiding implementation details and exposing essential functionalities.

6. I/O Processing

  • Object-oriented programming allows you to model input and output operations as objects.
  • For instance, a File object can represent a file on disk, with methods for reading, writing, and manipulating data.

Encapsulation and Data Abstraction: The Cornerstones of Objects

Encapsulation and data abstraction are fundamental concepts in object-oriented programming (OOP) that work together to define how objects function.

1. Encapsulation:

  • Imagine a capsule that holds medicine. The capsule protects the medicine (data) from external tampering. Similarly, encapsulation protects an object’s internal data (attributes) by restricting direct access.
  • Objects expose methods (behaviors) to interact with the data in a controlled way. This ensures data integrity and promotes code maintainability.
  • Access modifiers like public, private, and protected are used to control access to attributes and methods.

2. Data Abstraction:

  • Abstraction focuses on the essential details users need to interact with an object, hiding the underlying implementation complexities.
  • Think of a car. You interact with the steering wheel, pedals, etc., but don’t need to know how the engine works.
  • In OOP, abstraction is achieved through interfaces and abstract classes. Interfaces define functionalities objects must provide, while abstract classes provide partial implementations that subclasses can inherit.

3. The Concept of Objects:

– State: The current condition of an object, represented by its attributes (data) and their values.– Behavior: The actions an object can perform, implemented by its methods.– Identity: What makes a unique instance of a class. It’s often determined by a unique identifier or object reference.

4. Classes:

  • A class acts as a blueprint for creating objects. It defines the attributes and methods that all objects of that class will share.
  • Identifying classes involves recognizing real-world entities with similar attributes and behaviors. Examples: Car, Book, Customer.

– Attributes: These represent the properties of an object, like a car’s color, model, or speed.– Services (Methods): These define the functionalities an object can perform, like a car’s accelerate(), brake(), or turn() methods.

5. Access Modifiers:

  • Control the visibility and accessibility of attributes and methods within a class, across subclasses, and from other classes in the program:
    • public: Accessible from anywhere in the program.
    • private: Accessible only within the class itself.
    • protected: Accessible within the class and subclasses.

6. Static Members:

  • Static members (attributes or methods) belong to the class itself, not individual objects.
  • They are shared among all instances of the class and accessed using the class name, not the object reference. Example: Math.PI

7. Instances (Objects):

  • Individual objects are created from a class blueprint. Each object has its own set of attribute values and can call the methods defined in the class.

8. Message Passing:

  • Objects communicate by sending messages (method calls) to each other. This allows them to request services or exchange information.

9. Construction and Destruction of Objects:

  • A special method called a constructor is typically used to initialize an object’s state when it’s created.
  • Destructors, if implemented, handle the cleanup of resources when an object is no longer needed. However, in many languages like Java, garbage collection automates this process.

Relationships in Object-Oriented Programming (OOP)

Relationships between objects are crucial for building modular and reusable code in OOP. Here’s a breakdown of some key relationships:

1. Inheritance:

  • Purpose: Allows creating new classes (subclasses) that inherit properties and functionalities from existing classes (superclasses). This promotes code reuse and reduces redundancy.
  • Types of Inheritance:
    • Single Inheritance: A subclass inherits from one superclass.
    • Multilevel Inheritance: A subclass inherits from another subclass, forming a chain of inheritance.
    • Hierarchical Inheritance: Multiple subclasses inherit from a single superclass.
    • Multiple Inheritance (Language Dependent): A subclass inherits from multiple superclasses (not supported in all OOP languages like Java due to potential complexities).
  • ‘Is-a’ Relationship: This relationship signifies that a subclass “is a type of” its superclass. For example, ElectricCar is a type of Car.

2. Association:

  • A connection between objects of different classes. Objects can know about and interact with each other without a strict hierarchy.
  • Associations can be:
    • One-to-One: A single object from one class associates with a single object from another class (e.g., Order has one Customer).
    • One-to-Many: A single object from one class associates with multiple objects from another class (e.g., Customer has many Orders).
    • Many-to-One: Multiple objects from one class associate with a single object from another class (e.g., Course has many Students).
    • Many-to-Many: Multiple objects from one class associate with multiple objects from another class (e.g., Student enrolls in many Courses, and a Course can have many Students).

3. Aggregation:

  • A specific type of association where a whole (composite) object has one or more parts (component) objects. The parts can exist independently, but their lifespans are often tied to the whole.

4. Interfaces:

  • Define a contract (like a service agreement) that specifies what functionalities a class must provide. They don’t contain implementation details.
  • Classes can implement one or more interfaces, guaranteeing they provide the required functionalities. This promotes loose coupling and enables polymorphism (objects of different classes can be treated similarly if they implement the same interface).

5. Abstract Classes:

  • Act as blueprints that cannot be directly instantiated (used to create objects).
  • They define abstract methods (without implementation) that subclasses must implement.
  • Abstract classes are useful for defining common functionalities for a group of related classes while enforcing specific behaviors through the abstract methods.

1. Strings:

  • Strings are sequences of characters used to represent text data.
  • Common operations on strings include:
    • Concatenation (joining strings)
    • Indexing and slicing (accessing substrings)
    • Searching (finding characters or substrings)
    • Modification (changing characters or case)
  • String manipulation functions and libraries vary depending on the programming language.

2. Exception Handling:

  • Exception handling is a mechanism to manage errors and unexpected conditions that may arise during program execution.
  • It allows you to write robust code that can gracefully handle errors and prevent program crashes.
  • Common steps in exception handling:
    • Try block: Contains the code that might generate an exception.
    • Except block: Catches the exception and provides handling logic.
    • Finally block: Executes code regardless of whether an exception occurs (often used for cleanup tasks).

3. Introduction to Multithreading:

  • Multithreading allows a program to execute multiple threads concurrently.
  • A thread is a lightweight unit of execution within a process.
  • Multithreading can improve the responsiveness of a program by allowing it to perform multiple tasks simultaneously (e.g., downloading a file while using another application).
  • However, it introduces complexity in terms of synchronization and race conditions (when multiple threads try to access the same resource).

4. Data Collections:

  • Data collections are structured ways to organize and store data.
  • Common data collections include:
    • Arrays: Ordered collections of items of the same data type.
    • Lists: Similar to arrays but can hold elements of different data types and may be resizable.
    • Sets: Unordered collections of unique elements.
    • Dictionaries (Maps): Collections of key-value pairs for associating data with unique keys.
  • Choosing the right data collection depends on the specific needs of your program (e.g., needing fast random access or handling duplicate elements).

5. Case Studies:

– ATM (Automated Teller Machine):

  • Objects: Account, Card, Transaction, ATM
  • Functionality: User interacts with the ATM object to perform transactions (withdraw, deposit, etc.) on their account using their card.
  • Exception Handling: Account with insufficient balance, invalid card, network errors.
  • Data Collections: Lists or Maps to store account information, transaction history.

– Library Management System:

  • Objects: Book, Member, Loan, Library
  • Functionality: Members can borrow and return books, library manages due dates, fines, etc.
  • Exception Handling: Book not available, overdue loans, invalid member ID.
  • Data Collections: Maps to store book information (title, author, availability), member details (name, contact), and loan records.

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