Display error message when user inputs "0", cannot get out of "error" message

Question

Any idea on how I can fix this? I'm telling the user to enter the amount of numbers he would like to average. Of course as you can see in the code, if he inputs a 0 or a negative number I want it to flag the user to enter another number that is not 0 or a negative number. The problem is, once the user puts a 0 or a negative number, it gets stuck in that state and I have to terminate the program.

Help?

import javax.swing.JOptionPane;

public class TestProgTres 
{
    public static void main(String[] args) 
    {
         //Variable Declaration
         String ShowSome;
         String ShowSomeAgain;
         int z           = 0;
         double avg      = 0;
         double totalamt = 0;

         ShowSome = JOptionPane.showInputDialog("Enter the amount of numbers you would like to average"); 
         double AllNumbers = Double.parseDouble(ShowSome);

         while (AllNumbers < 1)
         {
             JOptionPane.showInputDialog("You cannot enter a negative or a 0.  Enter the amount of numbers you would like to average");
             AllNumbers = Double.parseDouble(ShowSome);
         }//end while

             if (AllNumbers > 0)
             {
                 double Numbers [] = new double [(int) AllNumbers];

                 for (z = 0; z < Numbers.length; z++)
                 {
                     ShowSomeAgain= JOptionPane.showInputDialog("Enter number " + (z + 1));
                     Numbers[z]=Double.parseDouble(ShowSomeAgain);

                     totalamt += Numbers[z];
                     avg = totalamt/AllNumbers;
                 }
             }

              JOptionPane.showMessageDialog(null, "The  of the numberes entered is " + avg);
        }//end main
}// end class

You're not assigning to ShowSome and are ignoring the results from JOptionPane.showInputDialog — MadProgrammer
– MadProgrammer, Commented Jul 29, 2014 at 4:35

Elliott Frisch · Accepted Answer · 2014-07-29 04:41:19Z

3

Well, it isn't the cleanest but this has a fairly important error,

ShowSome = JOptionPane.showInputDialog("Enter the amount of numbers "
    + "you would like to average"); 
double AllNumbers = Double.parseDouble(ShowSome);

while (AllNumbers < 1)
{
  JOptionPane.showInputDialog("You cannot enter a negative or a 0. "
      + "Enter the amount of numbers you would like to average");
  // HERE!
  AllNumbers = Double.parseDouble(ShowSome);
}//end while

You need to prompt for and update ShowSome.

while (AllNumbers < 1)
{
  // HERE!
  ShowSome = JOptionPane.showInputDialog("You cannot enter a negative or a 0. "
      + " Enter the amount of numbers you would like to average");
  // Get it again.
  AllNumbers = Double.parseDouble(ShowSome);
}//end while

Also, the Java naming convention would name your variables starting with a lower case letter. Using showSome would be easier to read ShowSome looks like a class name. Same with allNumbers.

edited Jul 29, 2014 at 4:41

answered Jul 29, 2014 at 4:30

Elliott Frisch

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2 Comments

MadProgrammer Over a year ago

As an alternative, a do-while loop might be a better structure to use, cause you want to do at least one iteration of the loop...just saying ... and why are you sowing the input dialog twice?

MadProgrammer Over a year ago

Know that feeling, looks better now +1

MadProgrammer · Accepted Answer · 2014-07-29 04:41:20Z

2

Basically, you want to ask the user at least once to enter a value, so why not just reduce the entire work load down to a single do-while loop, for example...

double AllNumbers = 0;
do {

    String ShowSome = JOptionPane.showInputDialog("Enter the amount of numbers you would like to average"); 
    AllNumbers = Double.parseDouble(ShowSome);
} while (AllNumbers < 1);

The main problem you're having with your current loop is you are ignoring the return value from the JOptionPane and continuously parsing what was previously entered...

// ShowSome is now set to, let's say 0...
ShowSome = JOptionPane.showInputDialog("Enter the amount of numbers you would like to average"); 
// AllNumbers  is now 0
double AllNumbers = Double.parseDouble(ShowSome);

while (AllNumbers < 1)
{
     // Prompting for a value, but you are ignoring it...
     JOptionPane.showInputDialog("You cannot enter a negative or a 0.  Enter the amount of numbers you would like to average");
     // Parsing ShowSome which is still 0 (as an example)...
     AllNumbers = Double.parseDouble(ShowSome);
 }//end while

answered Jul 29, 2014 at 4:41

MadProgrammer

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3 Comments

user3859018 Over a year ago

any idea on how to ensure that a user doesn't input a decimal or a letter? I want to make sure that what the user puts in is a whole number now that I am testing this program.

user3859018 Over a year ago

Quick question. I just did this: do { try { String ShowSome = JOptionPane.showInputDialog("Enter numbers."); AllNumbers = Integer.parseInt(ShowSome); } catch(NumberFormatException e) { JOptionPane.showMessageDialog(null, "Value must be an integer!"); } } How do I make it so when the user clicks cancel, the error message doesn't pop up?

MadProgrammer Over a year ago

From memory, if the user presses cancel or closes the dialog via the [x] button, JOptionPane will return null...

Akash Thakare · Accepted Answer · 2014-07-29 04:46:24Z

Move following code inside the loop to prompt for input every time when user enters wrong input and break loop while you get what you want.

     //Declare ShowSome and AllNumbers outside loop
     while (true){
          try{
            ShowSome = JOptionPane.showInputDialog("Enter....."); 
            AllNumbers = Double.parseDouble(ShowSome);
            //May Throw exception for invalid input So be careful with this 
            if(AllNumbers>=1)break;
            JOptionPane.showInputDialog("You cannot enter a negative or a 0"); 
          }catch(NumberFormatException e){
          JOptionPane.showInputDialog("Not a valid Number!"); 
          //Not Recommended to swallow the exception
          }
     }

Secondly there is no meaning of checking if (AllNumbers > 0) after doing this as above code will prompt until user enters wrong input so you will definitely get proper value which is >=1.

You should use try-catch mechanism to avoid Exception for invalid input.

Moreover you should declare AllNumbers as integer to avoid cast.

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