Principles of Object Technology

📘 Principles of Object Technology (OOAD)

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🔹 1. Definition

Object Technology refers to a way of designing and developing software using objects, which represent real-world entities. These objects contain data (attributes) and behavior (methods/functions).

👉 In simple words: Instead of writing long procedures, we break a system into smaller objects that interact with each other.

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🔹 2. Core Principles of Object Technology

These principles are the foundation of Object-Oriented Analysis and Design (OOAD).

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🔸 2.1 Abstraction

Definition: Abstraction means showing only essential features of an object and hiding unnecessary details.

Key Idea: Focus on what an object does, not how it does it.

Example: A Car object:

• You use steering, brakes, accelerator
• You don’t need to know how the engine works internally

Diagram Description: A simple box labeled Car with only relevant features like start(), stop().

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🔸 2.2 Encapsulation (Data Hiding)

Definition: Encapsulation is the process of wrapping data and methods together into a single unit (class) and restricting direct access to some components.

Key Idea: Protect data from outside interference.

Example:

BankAccount
- balance (private)
+ deposit()
+ withdraw()

Users cannot directly change balance, only through methods.

Rule: Use access modifiers:

• Private
• Public
• Protected

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🔸 2.3 Inheritance

Definition: Inheritance allows one class (child/subclass) to acquire properties and behavior of another class (parent/superclass).

Key Idea: Code reuse and hierarchical classification.

Example:

Vehicle (Parent)
  → Car (Child)
  → Bike (Child)

Types of Inheritance:

• Single
• Multiple
• Multilevel
• Hierarchical

Diagram Description: Tree structure showing parent → child relationship.

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🔸 2.4 Polymorphism

Definition: Polymorphism means one interface, multiple implementations.

Types:

1. Compile-time (Method Overloading)
2. Run-time (Method Overriding)

Example:

draw()
- draw(circle)
- draw(square)

Real-life Example: A person can be a teacher, father, or friend depending on context.

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🔸 2.5 Modularity

Definition: Breaking a system into smaller independent modules.

Key Idea: Each module handles a specific task.

Advantages:

• Easy to understand
• Easy to maintain
• Reusable

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🔸 2.6 Hierarchy

Definition: Arrangement of objects/classes in a tree-like structure.

Example:

Animal
 ├── Mammal
 ├── Bird

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🔸 2.7 Typing

Definition: Typing ensures that objects are used according to their defined data types and class structure.

Types:

• Strong typing
• Weak typing

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🔸 2.8 Concurrency

Definition: Ability of a system to handle multiple tasks simultaneously.

Example: Using multiple threads in a program.

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🔸 2.9 Persistence

Definition: Objects continue to exist even after program execution.

Example: Saving data in a database or file.

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🔹 3. Additional Supporting Concepts

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🔸 3.1 Class vs Object

Class	Object
Blueprint	Instance
Logical	Physical
Example: Car design	Actual car

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🔸 3.2 Message Passing

Definition: Objects communicate by sending messages (calling methods).

Example:

object1.method(object2)

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🔸 3.3 Association, Aggregation, Composition

Concept	Description
Association	General relationship
Aggregation	Weak "has-a" relationship
Composition	Strong ownership

Example:

• Car has Engine → Composition

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🔹 4. Advantages of Object Technology

• Reusability
• Flexibility
• Maintainability
• Scalability
• Real-world modeling

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🔹 5. Step-by-Step Example (Simple System)

👉 Problem: Design a Library System

Step 1: Identify objects

• Book, Member, Librarian

Step 2: Define attributes

• Book → title, author

Step 3: Define methods

• issueBook(), returnBook()

Step 4: Establish relationships

• Member borrows Book

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🔹 6. Important Rules / Key Points

• Always encapsulate data
• Prefer inheritance for reuse
• Use polymorphism for flexibility
• Keep modules loosely coupled
• Design for real-world mapping

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🔹 7. Likely Exam Questions

1. Define Object Technology and explain its importance.
2. Explain Abstraction with an example.
3. What is Encapsulation? How does it provide data security?
4. Describe Inheritance and its types.
5. What is Polymorphism? Explain with examples.
6. Differentiate between Class and Object.
7. Explain Association, Aggregation, and Composition.
8. What is Modularity and why is it important?
9. Explain Concurrency and Persistence.
10. Draw and explain a simple class hierarchy diagram.

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🔹 8. Quick Revision Summary 🧠

• Object Technology = System built using objects
• Abstraction → Show essentials only
• Encapsulation → Protect data
• Inheritance → Reuse code
• Polymorphism → Many forms
• Modularity → Divide system
• Hierarchy → Structured relationships
• Typing → Data correctness
• Concurrency → Multiple tasks
• Persistence → Data survives

👉 Remember: "A PIE MHTCP" Trick (A → Abstraction, P → Polymorphism, I → Inheritance, E → Encapsulation, M → Modularity, H → Hierarchy, T → Typing, C → Concurrency, P → Persistence)

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