having runtime error with java program

Question

I am given a list of 3 digit numbers and I am trying to see if they are in descending order. The number of elements in the list is not determined but I have set my SENTINEL value to be 1000.

The following error keeps happening though:

CompileRunTest: throwable = java.util.NoSuchElementException
java.util.NoSuchElementException

My code:

import java.util.Scanner ;

public class StrictDescending {

    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        final int SENTINEL = 1000 ;
        int firstValue = in.nextInt();
        while (firstValue < 1000)
        {
            int secondValue = in.nextInt() ;
            while(secondValue < 1000)
            {
                if(firstValue > secondValue)
                {
                    System.out.println("Yes, the list is in descending order.") ;
                }
                else
                {
                    System.out.println("No, the list is not in descending order.") ;
                }

                secondValue = in.nextInt();
            }

            firstValue = in.nextInt() ;
        }
    }

}

That error gets throw if there's no more input to consume. How are you testing it? — resueman
– resueman, Commented Jun 9, 2016 at 17:17
145 130 125 100 1000 and 145 130 130 125 1000 those are two different given inputs — javahelp
– javahelp, Commented Jun 9, 2016 at 17:17
Why declare the SENTINEL = 1000; if you aren't using it anywhere? — Orin
– Orin, Commented Jun 9, 2016 at 17:40

Josh Wilson · Accepted Answer · 2016-06-09 17:21:34Z

1

Try switching the first while to an if statement, add firstValue = secondValue on the line before secondValue = in.nextInt(); and remove the last firstValue = in.nextInt(); You'll need to mess around with your print statement a little as well.

As it is your program flow doesn't quite make sense since you will try to consume from stdin even when there are no numbers left.

answered Jun 9, 2016 at 17:21

Josh Wilson

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2 Comments

javahelp Over a year ago

okay i did that for the inputs 145 130 125 100 1000 and it gave me Yes, the list is in descending order (3 times repeated)

Josh Wilson Over a year ago

I'll let you figure that part out. I can't do all your homework for you ;)

LowLevel · Accepted Answer · 2016-06-11 08:10:42Z

0

EDITED ANSWER

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    int previousValue = getInt(sc);
    while(Math.abs(previousValue) < 1000) {
        if (previousValue <= (previousValue = getInt(sc))) {
            System.out.println("No, the list is not in descending order.");
            break;
        }
        System.out.println("Yes, the list is in descending order.");
    }
}

public static int getInt(Scanner sc) {
    if (sc.hasNextInt()) {
        return sc.nextInt();
    }
    sc.next();
    System.out.println("Type only numbers, please.");
    return getInt(sc);
}

If you want that the message prints after you stop typing numbers (by typing a value >= than 1000), the following could be a possible solution (equal values do not support descending order):

public static void main(String[] args) {
    Scanner sc = new Scanner(System.in);
    Integer previousValue = getInt(sc);
    boolean descending = false;
    while(previousValue != null) {
        Integer currentValue = getInt(sc);
        if (currentValue != null) {
            if (previousValue > (previousValue = currentValue)) {
                if (!descending) { // if not yet true
                    descending = !descending; // set true
                }
            } else {
                descending = false; // to print: "No, ..."
                previousValue = null; // to break the loop
            }
        } else {
            previousValue = currentValue; // it's actually null
        }
    }
    System.out.println((descending)
        ? "Yes, the list is in descending order." 
        : "No, the list is not in descending order.");
}

public static Integer getInt(Scanner sc) {
    if (!sc.hasNextInt()) {
        sc.next();
        System.out.println("Type only numbers, please.");
        return getInt(sc);
    }
    int input = sc.nextInt();
    return (Math.abs(input) < 1000) ? input : null;
}

edited Jun 11, 2016 at 8:10

answered Jun 9, 2016 at 18:03

LowLevel

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11 Comments

javahelp Over a year ago

I am trying to compare x amount of numbers, the x value isnt given

javahelp Over a year ago

says just a list of numbers

LowLevel Over a year ago

But do you mean it stops when next int is greater or equal to the previous one? Or maybe I don't understand the problem. I need more details.

LowLevel Over a year ago

@javahelp I'm sorry. You wrote 3 DIGIT numbers, and not 3 numbers ")

javahelp Over a year ago

thanks for your time so given a list of three digit integrs, i need to make sure the list is in strictly descending order, if a number is not in descending order it should stop and print out no, the numbers are not in descending order and consecutive numbers that are equal are not in descneding order

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