Lesson 20. Check the Number of Days in a Month with Switch ... Case | Learn Basic Java

To solve the problem of checking the number of days in a month using the switch statement in Java, before writing the code, you need to plan the steps clearly. Below are the detailed steps to solve this problem:

Steps to Solve the Problem

1. Determine the Input

   • The user will input two values: the month (1-12) and the year (which could be a leap year or not).
   • These values will be taken from the keyboard or the user interface.

2. Check the Validity of the Month

   • The month must be in the range from 1 to 12.
   • If the month value is invalid, an error message should be displayed, and the program should either terminate or ask the user to re-enter the value.

3. Handle Days in Fixed-Number Months

   • The months with a fixed number of days are:
     • January, March, May, July, August, October, and December have 31 days.
     • April, June, September, and November have 30 days.
   • Use the switch statement to handle these months.

4. Handle February

   • February has a variable number of days depending on whether it's a leap year.
   • You need to check if the year is a leap year:
     • A leap year is one that is divisible by 4, but not by 100, or divisible by 400.
     • If the year is a leap year, February has 29 days; otherwise, it has 28 days.

5. Display the Result

   • After determining the number of days in the month, print the result for the user, including:
   • The number of days in the given month and year.

6. Handle Errors (if any)

   • If the user inputs an invalid month (not between 1 and 12), the program should notify the user and terminate or prompt for re-entry.
   • If the entered year is invalid (such as a negative year), the program should handle it appropriately.

Writing the Code

Here is the Java code for the problem of checking the number of days in a month:

import java.util.Scanner;

public class DaysInMonth {
    public static void main(String[] args) {
        // Step 1: Input month and year
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter month (1-12): ");
        int month = scanner.nextInt();  // Input month

        System.out.print("Enter year: ");
        int year = scanner.nextInt();   // Input year

        // Step 2: Check the validity of the month
        if (month < 1 || month > 12) {
            System.out.println("Invalid month.");
            return; // Exit the program if the month is invalid
        }

        // Step 3: Declare a variable to store the number of days in the month
        int daysInMonth = 0;

        // Step 4: Handle the number of days in the month using the switch statement
        switch (month) {
            case 1: // January
            case 3: // March
            case 5: // May
            case 7: // July
            case 8: // August
            case 10: // October
            case 12: // December
                daysInMonth = 31;
                break;
            case 4: // April
            case 6: // June
            case 9: // September
            case 11: // November
                daysInMonth = 30;
                break;
            case 2: // February
                // Check for leap year
                if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)) {
                    daysInMonth = 29; // Leap year
                } else {
                    daysInMonth = 28; // Non-leap year
                }
                break;
        }

        // Step 5: Display the result
        System.out.println("The number of days in month " + month + " of year " + year + " is: " + daysInMonth);
    }
}

Run and Check the Results

After implementing the code, the program will prompt you to input the month and year to check the number of days in the month. Below are some examples and results when running the program:

Example 1:

• Input: Month = 2, Year = 2024
• Result: "The number of days in month 2 of year 2024 is: 29"
• Explanation: Since 2024 is a leap year, February has 29 days.

Example 2:

• Input: Month = 2, Year = 2023
• Result: "The number of days in month 2 of year 2023 is: 28"
• Explanation: 2023 is not a leap year, so February has 28 days.

Example 3:

• Input: Month = 4, Year = 2023
• Result: "The number of days in month 4 of year 2023 is: 30"
• Explanation: April always has 30 days in every year.

Example 4:

• Input: Month = 12, Year = 2025
• Result: "The number of days in month 12 of year 2025 is: 31"
• Explanation: December always has 31 days.

Example 5:

• Input: Month = 13, Year = 2025
• Result: "Invalid month."
• Explanation: The month must be between 1 and 12, so month 13 is invalid.

Summary of Steps to Perform

1. Input the month and year from the user.
2. Check the validity of the month (must be between 1 and 12).
3. Handle months with fixed days (31 or 30 days).
4. Check February and determine the number of days based on whether it's a leap year.
5. Print the result showing the number of days in the corresponding month.
6. Notify the user of errors if an invalid month is entered or if there are other errors.

Now, you can easily apply these steps to write code for the problem of checking the number of days in a month using switch case in Java!

Next post: Lesson 21. How to Use the For Loop in Java