🧑‍💻 Classes and Methods in Java – Explained with Examples

When you write programs in Java, everything revolves around classes and methods. They are the building blocks of Object-Oriented Programming (OOPs).

📦 What is a Class?

A class is like a blueprint or template for creating objects.

• It defines variables (data members) → the state of the object.

• It defines methods (functions) → the behavior of the object.

👉 Think of a class as a recipe. The recipe describes how to make a cake, but you can bake many cakes (objects) using it.

🛠️ What is a Method?

A method is a block of code inside a class that performs a specific task.

• Helps in code reusability

• Makes programs organized and readable

👉 Think of a method as a chef’s action in the recipe → mixing ingredients, baking, decorating.

✨ Syntax

Class in Java

class ClassName {
    // variables
    // methods
}

Method in Java

returnType methodName(parameters) {
    // code to execute
    return value; // optional
}

📖 Example: Class & Method in Action

class Car {
    // Data members (variables)
    String brand;
    int speed;

    // Method
    void drive() {
        System.out.println(brand + " is driving at " + speed + " km/h");
    }
}

public class Main {
    public static void main(String[] args) {
        // Creating objects
        Car car1 = new Car();
        car1.brand = "Tesla";
        car1.speed = 120;
        car1.drive();

        Car car2 = new Car();
        car2.brand = "BMW";
        car2.speed = 150;
        car2.drive();
    }
}

✅ Output

Tesla is driving at 120 km/h
BMW is driving at 150 km/h

🔑 Key Takeaways

• Class = Blueprint (defines variables + methods)

• Object = Real-world instance created from a class

• Method = Behavior/action of the class

• Classes & methods make code modular, reusable, and closer to real-world modeling

🎯 Real-World Analogy

• Class = Recipe 🍰

• Object = Cakes baked using recipe 🎂🎂🎂

• Method = Actions like mixing, baking, decorating 👩‍🍳

✅ With classes and methods, Java becomes powerful in simulating the real world inside code.

📘 Examples of Classes and Methods in Java

1️⃣ Student Example 🎓

class Student {
    // Variables
    String name;
    int age;

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

public class Main {
    public static void main(String[] args) {
        Student s1 = new Student();
        s1.name = "Amit";
        s1.age = 20;
        s1.displayInfo();

        Student s2 = new Student();
        s2.name = "Priya";
        s2.age = 22;
        s2.displayInfo();
    }
}

✅ Output:

Name: Amit, Age: 20  
Name: Priya, Age: 22  

👉 Shows how class → Student and method → displayInfo() work together.

2️⃣ Calculator Example 🔢

class Calculator {
    // Method with parameters
    int add(int a, int b) {
        return a + b;
    }

    int multiply(int a, int b) {
        return a * b;
    }
}

public class Main {
    public static void main(String[] args) {
        Calculator calc = new Calculator();

        System.out.println("Sum: " + calc.add(5, 3));
        System.out.println("Product: " + calc.multiply(4, 6));
    }
}

✅ Output:

Sum: 8  
Product: 24  

👉 Demonstrates methods with return values and parameters.

3️⃣ Bank Account Example 🏦

class BankAccount {
    String accountHolder;
    double balance;

    // Method to deposit money
    void deposit(double amount) {
        balance += amount;
        System.out.println(amount + " deposited. New balance: " + balance);
    }

    // Method to withdraw money
    void withdraw(double amount) {
        if(amount <= balance) {
            balance -= amount;
            System.out.println(amount + " withdrawn. New balance: " + balance);
        } else {
            System.out.println("Insufficient balance!");
        }
    }
}

public class Main {
    public static void main(String[] args) {
        BankAccount acc = new BankAccount();
        acc.accountHolder = "Ravi";
        acc.balance = 5000;

        acc.deposit(2000);
        acc.withdraw(1500);
        acc.withdraw(7000);
    }
}

✅ Output:

2000.0 deposited. New balance: 7000.0  
1500.0 withdrawn. New balance: 5500.0  
Insufficient balance!  

👉 A real-world simulation where methods define actions (deposit/withdraw).

4️⃣ Simple Greeting Example 👋

class Greeter {
    void sayHello(String name) {
        System.out.println("Hello, " + name + "! Welcome to Java.");
    }
}

public class Main {
    public static void main(String[] args) {
        Greeter g = new Greeter();
        g.sayHello("Sunita");
        g.sayHello("Rahul");
    }
}

✅ Output:

Hello, Sunita! Welcome to Java.  
Hello, Rahul! Welcome to Java.  

👉 Engages beginners with a friendly, relatable example.