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Methods & Code Organization - Reference Handout

What You'll Learn Today

  • How to organize code with methods
  • Declaring and calling methods
  • Using parameters and return values
  • Building a menu system

Methods in Java

  • Method: A block of code that does a specific task
  • Why use methods?
    • Organize code
    • Avoid repetition
    • Make code easier to read

Declaring a Method

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

Calling a Method

sayHello(); // prints Hello!

Parameters and Return Values

  • Parameter: Information you pass to a method
  • Return value: What a method gives back

Example:

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

int sum = add(3, 5); // sum is 8

Method Overloading

  • Two or more methods with the same name but different parameters

Example:

public static void print(int x) {
    System.out.println(x);
}
public static void print(String s) {
    System.out.println(s);
}

Mini-Exercises

  1. Write a method to multiply two numbers
  2. Write a method to print a welcome message
  3. Try calling your methods from main

Challenge: Menu System

  • Build a text-based menu (e.g., calculator, greeting, exit)
  • Use a method for each menu option
  • Call methods from main based on user choice

Example (Starter):

import java.util.Scanner;

public class MenuSystem {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while (true) {
            printMenu();
            int choice = scanner.nextInt();
            if (choice == 1) greet();
            else if (choice == 2) addNumbers(scanner);
            else if (choice == 0) break;
            else System.out.println("Invalid choice");
        }
    }
    public static void printMenu() {
        System.out.println("1. Greet");
        System.out.println("2. Add Numbers");
        System.out.println("0. Exit");
        System.out.print("Choose: ");
    }
    public static void greet() {
        System.out.println("Hello, intern!");
    }
    public static void addNumbers(Scanner scanner) {
        System.out.print("Enter first number: ");
        int a = scanner.nextInt();
        System.out.print("Enter second number: ");
        int b = scanner.nextInt();
        System.out.println("Sum: " + (a + b));
    }
}

Troubleshooting Tips

  • Method not found: Check spelling and parameters
  • Wrong result: Double-check your logic
  • Menu not working: Make sure to call the right method for each choice

End of Day Checklist

  • Used methods to organize code
  • Built a menu system
  • Participated in meeting
  • Asked at least one question

Homework (Optional)

Brainstorm: Project ideas for next week

Tomorrow's Preview: Project Work

  • Start building your own Java project!