Confusion with booleans & while/if loops

[Rachel Green]

I'm having a hard time finding the issue in my code. If it picks up that it's an invalid date, I can't get out of the loop by entering a valid date. I've been trying to mess with the operands and starting the booleans with false or true but I can't seem to get the input to be validated correctly.

            // Get the start date for rental
            System.out.println("Enter the start date of your rental in number "
                    + "format.");
            System.out.print("Month: ");
            rentalMonth = keyboard.nextInt();
            System.out.print("Day: ");
            rentalDay = keyboard.nextInt();
            System.out.print("Year: ");
            rentalYear = keyboard.nextInt();

            // Validate the rental date by setting booleans to true
            if (rentalDay >= 1 && rentalDay <= 31) {
                day = true;
            }
            if (rentalMonth >= 1 && rentalMonth <= 13) {
                month = true;
            }
            if (rentalYear >= 2015 && rentalYear <= 2050) {
                year = true;
            }

           // If date is invalid, prompt for new integers
            while (month == false || day == false || year == false) {
                System.out.println("Invalid date");
                System.out.println("Enter the start date of your rental in number "
                        + "format.");

                System.out.print("Month: ");
                rentalMonth = keyboard.nextInt();
                System.out.print("Day: ");
                rentalDay = keyboard.nextInt();
                System.out.print("Year: ");
                rentalYear = keyboard.nextInt();
            }

           // If date is valid, return the values to user
            if (month == true && day == true && year == true) {
                System.out.println("Rental will start on: " + rentalMonth
                        + "/" + rentalDay + "/" + rentalYear);
            }

[Carey Brown]

You have 3 'if' statements checking the validity of the inputted date but this check only appears outside of the loop. Inside the loop you input a new date but it doesn't validate that date.

[Rachid Bou]

You have to re-validate month, day, and year inside the loop again, right after the keyboard entries:

       // If date is invalid, prompt for new integers
        while (month == false || day == false || year == false) {
            System.out.println("Invalid date");
            System.out.println("Enter the start date of your rental in number "
                    + "format.");

            System.out.print("Month: ");
            rentalMonth = keyboard.nextInt();
            System.out.print("Day: ");
            rentalDay = keyboard.nextInt();
            System.out.print("Year: ");
            rentalYear = keyboard.nextInt();
            
            // Validate the rental date by setting booleans to true
            if (rentalDay >= 1 && rentalDay <= 31) {
                day = true;
            }
            if (rentalMonth >= 1 && rentalMonth <= [color=red]13[/color]) {
                month = true;
            }
            if (rentalYear >= 2015 && rentalYear <= 2050) {
                year = true;
            }
        }

Also,  you should put the repeated code inside functions or by changing your logic, so the code is more reusable and less repetitive.


I did the following test:

import java.util.Scanner;

public class TestClass {

	public static void main(String[] args) {
		
		Scanner keyboard = new Scanner(System.in);
        int rentalMonth;
        int rentalDay;
        int rentalYear;
        boolean validDate = false;
        
       // If date not entered yet or invalid, prompt for new integers.
        while (!validDate) {
        	// Get the start date for rental
            System.out.println("Enter the start date of your rental in number "
                    + "format.");

            System.out.print("Month: ");
            rentalMonth = keyboard.nextInt();
            System.out.print("Day: ");
            rentalDay = keyboard.nextInt();
            System.out.print("Year: ");
            rentalYear = keyboard.nextInt();
            
            // Validate the rental date
            if ( (rentalMonth < 1 || rentalMonth > 12) || (rentalDay < 1 || rentalDay > 31) || (rentalYear < 2015 || rentalYear > 2050) ) {
            	//valideDate stays set to false;
            	System.out.println("Invalid date");
            } else {
            	validDate = true; //date is valid. will get out of the loop after the while condition is checked.
                // If date is valid, return the values to user
                System.out.println("Rental will start on: " + rentalMonth
                        + "/" + rentalDay + "/" + rentalYear);
            }
        }
	}
}

[Campbell Ritchie]

Also, I would suggest you get rid of the if blocks. Let's imagine you have entered day=23 month=11 year=2016 and run through the loop. At that point all your three booleans are set to true.
Let's imagine you now go round the loop again and do the validation again. Let's imagine you enter day=99 month=11 year=2016. The month and year if statements will run normally setting their booleans to true, i.e. the same as before, but the day if statement will never run. So is the day boolean going to be left at true?

I think you are better using a straight assignment:-
day = rentalDay >= 1 && rentalDay <= 31;
Avoid writing magic numbers like 31. Better style is to set up a constant
private static final int MAX_DAYS_IN_MONTH = 31;
0, 1 and −1 are permissible as number literals. Then you write
day = rentalDay >= 1 && rentalDay <= MAX_DAYS_IN_MONTH;
You might consider changing the names of those booleans. When you have rentalDay and day, it is obvious that day is going to be a number. Something like dayValid would sound better. It is a case where you can make life so much easier for yourself with judicious choice of variable names. And you can make life so much more difficult for yourself with injudicious choice of variable names. You might consider a single boolean, maybe dateValid. Then you can try this after you have set dateValid for the day
dateValid = dateValid && rentalMonth >= 1 && rentalMonth <= MAX_MONTH; /* etc. */
Avoid == true and == false like the plague. They are poor style and I shall let you work out the error they are prone to.
Not if (valid == true) ... but if (valid) ...
Not if (valid == false) ... but if (!valid) ...
Note the bang sign ! for not can be difficult to read. And <= or >= are harder to read than < >. Consider changing the name of your boolean. Can the program become easier to read if you don't work out dateValid at all? What if you work out dateWrong?

[Campbell Ritchie]

...and welcome to the Ranch