Problems with While loop execution

[Kevinius]

I have a problem with the second while loop shown below. The guidelines I was given was that my variable 'speed' cannot be a negative number. So I make this a condition in my while loop. If a negative number is entered, it prompts the user to enter a number greater than or equal to 0. That's all fine and dandy...my problem is that if the user inputs a non-negative number it is ignored. Am I missing something??

Here is the part of code in question:

public class Demo {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.print("Enter the speed: ");

        while(!in.hasNextInt()){
            System.out.println("Error: That was not a number!" + " '" + in.nextLine() + 
                    "'" + "\nEnter the speed: ");
        }
        int speed = in.nextInt();
        while (speed < 0) {
            System.out.println("Enter a number greater or equal to 0: " + in.nextLine());
        }

        SpeedHours speedHours = new SpeedHours(speed);
        System.out.println("The speed is: " + speedHours.getSpeed());
    }
}

Any advice is greatly appreciated!

[Junky]

Where do you assign a new value to speed?

[Kevinius]

I was just going to say that I tried that, but maybe I didn't do it correctly. After you mentioned that, I redefined "speed" and ran it. It works. I'm such a noob that it's obvious! Thank you much!

[Junky]

Are you sure it works?

What happens if I enter: -10 dammit

[Kevinius]

It definitely works! I put -10 in and it prompted me for a number greater than or equal to 0, so I put -10 in again. Same result. Then I put in 5, and it broke cleanly!

[Kevinius]

Now I can move on to the next segment of loops that is very similar. Then I'll have to use a GUI to output all the information.

[Junky]

But what about my input?

-10 dammit

That will crash your program.

[Kevinius]

-10 didn't crash my program at all. This is the result:

Enter the speed: -10
Enter a number greater or equal to 0: 
-10
Enter a number greater or equal to 0: 
-10
Enter a number greater or equal to 0: 
5
The speed is: 5
BUILD SUCCESSFUL (total time: 9 seconds)

[Junky]

GAH!

Can you see past the -10 to the dammit? I'm saying try enterering "-10" as the first input and then "dammit" as the second input.

[Kevinius]

Junky...sorry it took me awhile to realize what you were asking. I edited my code to look like this:

public class Demo {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        System.out.print("Enter the speed: ");

        while(!in.hasNextInt()){
            System.out.println("Error: That was not a number!" + " '" + in.nextLine() +
                    "'" + "\nEnter the speed: ");
        }
        int speed = in.nextInt();
        while (speed < 0) {
            System.out.println("Enter a number greater or equal to 0: " + in.nextLine());
            while (!in.hasNextInt()){
                System.out.println("Error: That was not a number!" + " '" + in.nextLine() +
                    "'" + "\nEnter the speed: ");
            }
         speed = in.nextInt();
        }
        
        SpeedHours speedHours = new SpeedHours(speed);
        System.out.println("The speed is: " + speedHours.getSpeed());
    }
}

And this was the result:

Enter the speed: -10
Enter a number greater or equal to 0: 
dammit
Error: That was not a number! 'dammit'
Enter the speed: 
5
The speed is: 5
BUILD SUCCESSFUL (total time: 11 seconds)

[Junky]

OK you managed to fix your code but notice how your loop checking for non-numbers is repeated in your code. A further exercise can be to see how you can modify it to eliminate the repeated code. One way is to only use a single loop.

while input is invalid {
    // get input and check it
}

[Kevinius]

Okay...here is what I came up with. Is this what you were referring to?

public class Demo {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);
        
        System.out.print("Enter the speed: ");

        boolean invalidInput = false;
        // Checks the input of the user
        while(!invalidInput){
        // If input is not an integer, prints error message and prompts user to re-enter.
            while(!in.hasNextInt()){
                System.out.println("Error: That was not a number!" + " '" + in.nextLine() +
                    "'" + "\nEnter the speed: ");
            }
            int speed = in.nextInt();
        // If speed < 0, prints error message and prompts user to re-enter.
        // If correct input entered, int speed is redefined.
            while (speed < 0){
                    System.out.println("Enter a number greater than or equal to 0: " + in.nextLine());
                    speed = in.nextInt();
            }
        // Prompts user to enter hours.
            System.out.println("Enter the hour(s): ");
        // If input is not an integer, prints error and prompts user to enter valid integer.    
            while(!in.hasNextInt()){
                System.out.println("Error: That was not a number!" + " '" + in.next() +
                        "'" + "\nEnter the hour(s): ");
            }
            int hours = in.nextInt();
        // If hours < 1, prints error message and prompts user to re-enter.
        // If correct input entered, int hours is redefined.
            while (hours < 1){
                System.out.println("Enter a number greater than or equal to 1: " + in.nextLine());
                hours = in.nextInt();
            }
        // New object speedHours created.
            SpeedHours speedHours = new SpeedHours(speed, hours);
        // Outputs the data entered, and displays the distance travelled.    
            System.out.println("The speed is: " + speedHours.getSpeed() + " miles per hour." +
                    "\nThe time is: " + speedHours.getHours() + " hours." +
                    "\nThe distance travelled is: " + speedHours.getDistance() + " miles.");
            }

      }
        
        
}

I've added some other code with this. Hopefully it's not too confusing. If I overdid the comments let me know.

[Kevinius]

I just realized that it still crashes...I'll chaulk it up to not knowing what the hell I'm doing! haha