NumberFormatException

**BurntCandy** · 10-09-2012, 01:39 AM

Hi all,
I am experiencing a problem handling a NumberFormatException in my code.

Java Code:

double getPrincipal(){
		double test = Double.parseDouble(JOptionPane.showInputDialog(null, "enter a principal between 1 and 500,000"));
		if(test > 0 && test < 500001){
		} else this.getPrincipal();
		return test;
	}

If someone types a string instead of a number into the dialog box I get a number format exception. Is there any way to check if Double.parseDouble worlds before using it. I have tried a try/catch but that messed everything up because the variables were not local.

Help?

**Fubarable** · 10-09-2012, 02:04 AM

Originally Posted by BurntCandy

...I have tried a try/catch but that messed everything up because the variables were not local.

That's the solution. You must fix the errors that you're now seeing. If you need help, show the code and errors to us.

**BurntCandy** · 10-09-2012, 02:55 AM

Java Code:

double getPrincipal(){
		try{
		double test = Double.parseDouble(JOptionPane.showInputDialog(null, "enter a principal between 1 and 500,000"));
		if(test > 0 && test < 500001){
		} else this.getPrincipal();
		return test;
		}catch (NumberFormatException bad){
			this.getPrincipal();
		}
		
	}

It is now giving me an error saying that I need to add a return or change the return type to void but I only want it to return once I get a value in between 0 and 500000 so I don't want to add one elsewhere

**BurntCandy** · 10-09-2012, 02:58 AM

i have also tried this

Java Code:

double getPrincipal(){
		double test; 
		try{
			Double.parseDouble(JOptionPane.showInputDialog(null, "enter a principal between 1 and 500,000"));
		} catch (NumberFormatException a){
			this.getPrincipal();
		}
		if(test > 0 && test < 500001){
		} else this.getPrincipal();
		return test;
		
	}

but it tells me that I need to initialize test. When I initialized test to a value it ended up only returning the value it was initialized to.

**Fubarable** · 10-09-2012, 03:03 AM

If there were my method, I don't think I'd try to solve it using recursion (having the method call itself). Instead I'd use a while loop, and only exit the loop when a decent value has been entered. something like (in pseudocode):

Java Code:

method getPrinciple 
  declare a double dummy variable, test, and set it to a default value of 0.0.
  declare a boolean testInvalid and set to true
  while testInvalid 
    try block
      get input and parse it to double
      // if I'm at this line, the parse was successful!
      check if test is in the valid range
      if so, return test
      if not, tell the user that the number entered was out of range to try again.
    catch for NumberFormatException
      tell the user that they need to enter a valid number.
    end of try/catch block
  end while loop
end of method

Actually you don't even need a boolean variable here and can simply use while (true) since my loop ends by returning a valid value from the method from within the while loop.