Java validation help needed

[AdRock952]

I have some validation that checks for numerical input and displays an error message if anything else is entered.

What I want is, if the user enters a negative number, an error message is displayed also and asks again for input until they enter a positive number.

Everything I try lets the user enter a negative number

Here is my vallidation code



boolean wrongValue = true; //

//Prompt user to enter a weight for the package
System.out.print("Enter a package weight (kg) or press 0 to exit: ");

//while the value given to packageWeight is wrong, keep doing this loop.
while(wrongValue)
{
try
{
//Assign the value entered from the keyboard to packageWeight
packageWeight = new Double(keyboardInput.readLine()).doubleValue();

//Set boolean variable wrongValue to false so it can escape the loop
wrongValue = false;
}
catch (NumberFormatException e)
{
//Prompt user to enter a weight for the package

System.out.print("Enter a package weight (kg) or press 0 to exit: ");
}
}

 

[Diancecht]

Some ideas:

- Use code tags when posting code.
- You don't check if value is greater than zero

Cheers,
Dian

 

[AdRock952]

I couldn't find code tags anywhere on the page otherwise I would have done that

Underneath the validation I have this <b>while (packageWeight != 0) { more code }</b> which goes to the next part of the code if what is entered is any number but zero. Unfortunately negative numbers are still valid inout but I want to make it invalid

 

[sedj]

Your using an integer to compare to a double.

Possibly something like this :

          do
          {
             System.out.print("Enter a package weight (kg) or press 0 to exit: ");
             
             try
             {
                 //Assign the value entered from the keyboard to packageWeight
                packageWeight = new Double(keyboardInput.readLine()).doubleValue();           
             }
             catch (NumberFormatException e)
            {
             	
                packageWeight = 1.0; //push them back to the prompt
                
            }    
          } while (packageWeight > 0.0);

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[Diancecht]

That will end if the user enters a negative value, you need to change the assignmet to -1.0 and change the comparison.

Cheers,
Dian

 

[jstreich]

That will end if the user enters a negative value, you need to change the assignmet to -1.0 and change the comparison.

Sedj is spot on. == for float doesn't always work, and
while(packageWeight > 0.0) is false for 0. If he needs exactly 0, then he needs to check while(packageWeight > 0.0 && packageWeight < 0.0)[/red] becuase "is both naïve and dangerous to test two floating point values for strict equality" -Sun.

You may argue that he's also excluding negative numbers, but negative weight doesn't make sense as weight is not a vecotor. Personally, I'd consider negative an error condition.

"you need to change the assignmet to -1.0", why?

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[Diancecht]

OP wants the program to iterate until the user enters a positive number. Sedj's sollution will do that, but with negative numbers.

Cheers,
Dian