recognize string as input and throw exception if not an integer

Question

I'm new to java and was trying to do this program. Basically entering 3 numbers, it will calculate the volume of a cube. If a negative number is typed then it will throw an exception, and also when there are more then 3 input. I wanted it to throw an exception also, if the input is not a number, but I have no idea how to store the input inside a variable and then check if it's a string and eventually throw an exception. Any suggestions? Here's my code

     public class CubeVolume
     {
       public static void main(String [] args)
       {
         try
         {
           // try if there is more than 3 arguments 
           int width = Integer.parseInt(args[0]);
           int depth = Integer.parseInt(args[1]);
           int hight = Integer.parseInt(args[2]);
           if (args.length > 3)
           throw new ArrayIndexOutOfBoundsException
                 ("You have supplied " + args.length + " arguments!");

          // try if there is less than 3 arguments
          if (args.length < 3)
          throw new ArrayIndexOutOfBoundsException
              ("You have supplied " + args.length + " arguments!");                    

          // checks if the width entered is equal or less than 0
          if (width <= 0)
          throw new NumberFormatException
              ("The argument " + width + " is a negative number!");

          // checks if the depth entered is equal or less than 0
          if (depth <= 0)
          throw new NumberFormatException
              ("The argument " + depth + " is a negative number!"); 

          // checks if the hight entered is equal or less than 0
          if (hight <= 0)
          throw new NumberFormatException
              ("The argument " + hight + " is a negative number!");     


          int volume = width * depth * hight;
          System.out.println("The volume of a cube with dimensions " + "(" + width 
                             + "," + hight + "," + depth + ") " + "is " + volume);
         } // try

        // if there's one than more argument error will be displayed
        catch (ArrayIndexOutOfBoundsException exception)
        {
          System.out.println("Please supply width, depth and hight arguments!");
          System.out.println("Exception message was: '" + exception.getMessage() 
                             + "'");
          System.err.println(exception);
        } // catch          

       // if a negative number is entered error will be displayed
       catch (NumberFormatException exception)
       {
         System.out.println("Dimensions for a cube can't be negative, please "
                                   + "insert only positive whole numbers!");
         System.out.println("Exception message was: '" + exception.getMessage() 
                                   + "'");     
         System.err.println(exception);
       } // catch

     } // main
  } // CubeMain

After glancing at the code I don't see any obvious errors. What problems are you having, specifically? Have you tried running it? — jgitter
– jgitter, Commented Feb 25, 2014 at 21:16
there's no problem, but I want to throw an exception if the input is not a number. So if it's a string would display an error message saying that is not possible to use a string, and I have no clue how to do it. — user3353167
– user3353167, Commented Feb 25, 2014 at 21:18
If you look at the spec, Integer.parseInt throws a NumberFormatException if the string does not contain a parsable integer. The only question would be whether you wanted to check for "junk" after the number, I think. — Hot Licks
– Hot Licks, Commented Feb 25, 2014 at 21:20
Integer.parseInt() throws an exception for you if the string is not an integer. You can catch it and throw your own custom exception if you want. Side note: You're checking that the length is 3 after having already accessed the 3rd argument. — JB Nizet
– JB Nizet, Commented Feb 25, 2014 at 21:21
How can i take the input from the console and check if it's not a number and throw an exception? because with that code if I enter a string, it will throw an exception giving the message: Dimensions for an object can't be negative, please insert only positive whole numbers! java.lang.NumberFormatException: For input string: "ciao" Exception message was: 'For input string: "ciao"' — user3353167
– user3353167, Commented Feb 25, 2014 at 21:36

jgitter · Accepted Answer · 2014-02-25 22:15:35Z

3

This:

int width = Integer.parseInt(args[0]);

already throws a NumberFormatException if the String in question is not a valid string representation of an integer.

EDIT:

To address your comments:

public class CubeVolume {
   private int width;
   private int depth;
   private int height;

   public static void main(String [] args) {
       if (args.length != 3) {
           throw new Exception("Width, height and depth are required arguments");
       }
       width = Integer.parseInt(args[0]);
       depth = Integer.parseInt(args[1]);
       height = Integer.parseInt(args[2]);

       // more stuff here
   }
}

edited Feb 25, 2014 at 22:15

answered Feb 25, 2014 at 21:19

jgitter

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16 Comments

user3353167 Over a year ago

is it possible to do throw a custom exception?

jgitter Over a year ago

Also, I highly recommend that you don't "repurpose" existing java exceptions. Either throw generic Exceptions or create new specific exception classes.

jgitter Over a year ago

Yes, it is possible to throw custom exceptions. Just create a class that extends Exception. .... Then throw it.

user3353167 Over a year ago

if I run it and let's say i type 'hello' into the console, it will catch the exception for the negative numbers, so it will display: Dimensions for an object can't be negative, please insert only positive whole numbers! java.lang.NumberFormatException: For input string: "ciao" Exception message was: 'For input string: "ciao"'

jgitter Over a year ago

that is because you are catching NumberFormatException in your outer try/catch block and throwing a new exception with a different message.

|

Manoj Shrestha · Accepted Answer · 2014-02-25 22:19:59Z

-1

You can create your own exception class and throw the instance of that class from a method.

The exception class:

// Extending Exception makes your class throwable
class MyException extends Exception {

    public MyException( String string ) {
        super( string );
    }
}

And for parsing the input string to integer, call a method like this :

int width = parseInt(args[0]);

where your parseInt() method throws your custom exception as follows:

    private int parseInt( String number ) throws Exception {
        try {
            return Integer.parseInt( number );
        } catch ( Exception e ) {
            throw new MyException( "The input is not a number" );
        }
    }

Now, you can catch your custom exception MyException similar to other standard exceptions:

       // catching your custom exception
       catch ( MyException e ) {
            System.err.println( e );
        }

        // if there's one than more argument error will be displayed
        catch (ArrayIndexOutOfBoundsException exception)
        {
          System.out.println("Please supply width, depth and hight arguments!");
          System.out.println("Exception message was: '" + exception.getMessage() 
                             + "'");
          System.err.println(exception);
        } // catch          

       // if a negative number is entered error will be displayed
       catch (NumberFormatException exception)
       {
         System.out.println("Dimensions for a cube can't be negative, please "
                                   + "insert only positive whole numbers!");
         System.out.println("Exception message was: '" + exception.getMessage() 
                                   + "'");     
         System.err.println(exception);
       } // catch

edited Feb 25, 2014 at 22:19

answered Feb 25, 2014 at 22:08

Manoj Shrestha

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2 Comments

MirroredFate Over a year ago

-1 Don't catch the general Exception class. Also, creating an unique class is redundant as it is doing the same thing as the NumberFormatException. Also, I have no idea when you would ever catch a NumberFormatException given your code.

user3353167 Over a year ago

is it possibile to do it within one class? and if yes, could you show me how please?

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