NumberFormatException

[Candy Bortniker]

I am getting this exception when my textfield is empty. What can I do to fix the problem? I start out with numbers in getText() but when I remove the last one I get the exception. This is the code where the error is happening.

protected void postRemoveUpdate ( DefaultDocumentEvent evt )
{
super.postRemoveUpdate ( evt );
//System.out.println ( "Document has had data removed" );
long text = Long.parseLong(ltc.getText());
System.out.println("the value of the text field is " + text);
total = total - Integer.parseInt(String.valueOf(text));
System.out.println("total = " + total);
if ( ltc.getMinimum() <= total && total  <= ltc.getMaximum() )
ltc.setBackground ( Color.green );
else if ( total  > ltc.getMaximum() )
ltc.setBackground ( Color.red );
else 
ltc.setBackground ( Color.cyan); 
}
  

[Ernest Friedman-Hill]

Any time you use Long.parseLong() or any similar method that turns a String into a number, you face the possibility that the String isn't a valid number. All such Java methods report this problem by throwing a NumberFormatException. You need to catch the exception and do one of two things: report the error to the user (if they typed in invalid input) or substitute a default value (if you want non-numbers to be equal to 0, for example.) The latter strategy would look like

long text;
try {
  text = Long.parseLong(ltc.getText());
} catch (NumberFormatException nfe) {
  text = 0;
}

By the way, I can't help but remark that having a variable of type "long" named "text" makes my head hurt. Well-chosen variable names go a long way towards making code easier to write and to read.
Now, what is going on with the following line of code?

total = total + Integer.parseInt(String.valueOf(text));

You've parsed a String to create a long, and now you're turning the long into a String and then parsing it as an int -- why? Why not simply

total = total + (int) text;