How to check is value entered is less than zero

[AdRock]

I have some code that validate suser input and checks that they enter 0 and over but i need something to check that the user doesn't enter -1 or something. Currently the code would let them carry on and i don't want that.

How would i check for this input....would I use and if statement within the try block?

Here is the 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: ");
         	}
}

[masher]

would I use and if statement within the try block?

Why don't you try it and see?

[sjalle]

Yes, and if negative, issue an error message and... continue;

[AdRock]

I tried using an If statment within the try block with an error message but it is still going onto the next part even though wrongValue is false

[KatyMc238]

Im not sure but does while(wrongvalue){..... do anything at all?? Surely that condition just means that "while wrongvalue has a value"..

If you put while(wrongvalue==false){.... that might work

[AdRock]

At the moment if the user enters anything but a positive number or 0 then it catches a number format exception, but because -1 is a legitimate number it exits the loop and carries on as normal.

Anthing less than 0 can't have a weight so I want to prevent the user entering anything less than 0

I have tried this but it still doesn't catch anything less than 0

boolean wrongValue = true;	//

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

      	while(wrongValue)
      	{
         	try
         	{	
            	packageWeight = new Double(keyboardInput.readLine()).doubleValue();
            
            	wrongValue = false;
         	}
         	catch (NumberFormatException e)
	         {
	            System.out.print("Enter a package weight (kg) or press 0 to exit: ");
         	}
      	}

		while (packageWeight != 0 && packageWeight <0)
		{

[masher]

Im not sure but does while(wrongvalue){..... do anything at all?? Surely that condition just means that "while wrongvalue has a value"..

If you put while(wrongvalue==false){.... that might work

It works. The expression in the brackets after 'while' is evaluated to a boolean.

So, while(num > 0) will continue to loop while num is greater than 0, as num > 0 will be true. As wrongValue is already a boolean, there is no need to have a equality or other operator, as the reassignment of wrongValue to true/false occurs inside the loop.

[masher]

You could do this:

      //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();

            if(packageWeight < 0)
            {
               throw new NumberFormatException();// or you could define your own exception...
            }
            else
            {
               //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: ");
         }
      }

I don't know how legitimate it is to throw exceptions, but you could always define your own NumberLessThanZeroException class, and throw that...