Java Programming Lesson-11 | Object-Oriented Programming (OOP) — Classes & Objects

Java Programming Lesson-11

Now we dive into Lesson-11: Object-Oriented Programming (OOP) — Classes & Objects, the core of Java.

OOP is essential for writing professional, reusable, and organized code.

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📘 Lesson-11 — Classes & Objects in Java

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✅ What is a Class?

A class is like a blueprint for an object.
It defines attributes (variables) and behaviors (methods).

class Car {
    String color;
    String model;

    void drive() {
        System.out.println("Car is driving");
    }
}

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✅ What is an Object?

An object is an instance of a class — like a real car built from blueprint.

Car myCar = new Car(); // Create object
myCar.color = "Red";
myCar.model = "Toyota";

myCar.drive(); // Call method

✅ Output:

Car is driving

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✅ Anatomy of a Class

Part	Meaning
Fields / Attributes	Variables storing state (e.g., color, age)
Methods / Functions	Behavior (e.g., drive(), start())
Constructor	Special method to initialize object

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✅ Constructor (Initialize Object)

class Car {
    String model;
    int year;

    // Constructor
    Car(String m, int y) {
        model = m;
        year = y;
    }

    void display() {
        System.out.println("Model: " + model + ", Year: " + year);
    }
}

public class Main {
    public static void main(String[] args) {
        Car car1 = new Car("Toyota", 2023);
        car1.display();
    }
}

✅ Output:

Model: Toyota, Year: 2023

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✅ Accessing Object Members

class Student {
    String name;
    int age;

    void showInfo() {
        System.out.println("Name: " + name + ", Age: " + age);
    }
}

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student();
        s1.name = "Jitu";
        s1.age = 21;
        s1.showInfo();
    }
}

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✅ Key Points About Objects

✔ Each object has its own copy of attributes
✔ Methods can access object data
✔ Multiple objects can be created from same class

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✅ Example: Multiple Objects

Student s1 = new Student();
s1.name = "Alice"; s1.age = 20;

Student s2 = new Student();
s2.name = "Bob"; s2.age = 22;

s1.showInfo(); // Name: Alice, Age: 20
s2.showInfo(); // Name: Bob, Age: 22

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📝 Exercise for You ✅

Create a program:

1️⃣ Create class Book with attributes: title, author, price
2️⃣ Create a constructor to initialize values
3️⃣ Add method display() to print book info
4️⃣ Create 2 book objects and display their info

Example Output:

Title: Java Basics, Author: Jitu, Price: 500
Title: Advanced Java, Author: Hasan, Price: 750

Reply with:
✅ Your Code
✅ Output

I’ll check & give feedback 🔥

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🎯 Quick Quiz

1️⃣ Which keyword creates an object?
A) class
B) new
C) object

2️⃣ What is a blueprint in Java OOP?
A) Object
B) Class
C) Method

Reply like:
1 → ?, 2 → ?

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✅ Lesson-11 Completed!

✅ NEXT PART - Lesson-12: Inheritance & Polymorphism.