Methods: Building Reusable Blocks of Code

As your programs get bigger, writing everything inside the main method becomes messy and hard to manage. Methods allow you to group a block of code together, give it a name, and run it whenever you need it.

Think of a method like a recipe: you define the steps once, and you can "cook" it as many times as you want.

1. Anatomy of a Method

A basic method consists of a header and a body.

public static int addNumbers(int a, int b) {
    // Body: The code to execute
    int sum = a + b;
    return sum; 
}

The Breakdown:

• public static: For now, we use these keywords so we can call the method directly from our main class.
• Return Type (int): This tells Java what kind of data the method gives back. If it gives nothing back, we use void.
• Method Name (addNumbers): Use camelCase to describe what the method does.
• Parameters (int a, int b): These are inputs the method needs to do its job.
• return: This keyword sends the result back to whoever called the method.

2. Calling a Method

Once a method is defined, you "call" it by using its name followed by parentheses.

public class Main {
    public static void main(String[] args) {
        // Calling the method and storing the result
        int result = addNumbers(5, 10);
        System.out.println("The sum is: " + result);
    }

    public static int addNumbers(int a, int b) {
        return a + b;
    }
}

3. Void Methods (No Return)

Sometimes you just want a method to perform an action (like printing text) without sending a value back. For this, we use the void return type.

public static void sayHello(String name) {
    System.out.println("Hello, " + name + "!");
}

// Called as: sayHello("Ahmed");

4. Why Use Methods?

1. DRY (Don't Repeat Yourself): Instead of writing the same logic 10 times, write one method and call it 10 times.
2. Readability: It’s easier to read calculateTax() than 20 lines of math.
3. Maintainability: If you need to change how the tax is calculated, you only have to change it in one place.

💻 Full Practical Example: The Area Calculator

Copy this code to see how different methods can be used together:

import java.util.Scanner;

public class Geometry {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);

        displayWelcome();

        System.out.print("Enter the radius of your circle: ");
        double r = input.nextDouble();

        double area = calculateArea(r);
        System.out.printf("The total area is: %.2f %n", area);

        input.close();
    }

    // A void method with no parameters
    public static void displayWelcome() {
        System.out.println("Welcome to the Geometry Tool!");
        System.out.println("----------------------------");
    }

    // A method that takes a double and returns a double
    public static double calculateArea(double radius) {
        return Math.PI * Math.pow(radius, 2);
    }
}

💡 Challenge: The Temperature Pro

Create a program with two methods:

1. toCelsius(double fahrenheit): Returns the converted temperature.
2. checkWeather(double celsius): A void method that prints "Cold" if the temp is below 15, and "Warm" if it's 15 or higher.

Call both from your main method!