Thread: int / double validation

I have 95% of my code written but cannot figure out how to set up the error checking for when the user enters letters in a field that requires numbers.

Assignment : Create an interactive gui program that converts miles to kilometers and vice versa, dependent on what the user chooses. Also requires error checking for input other than integers or doubles.

Here is my code thus far.
[highlight = java]

import javax.swing.JOptionPane;
 
public class Converter
 
{
 
 
 
 
	public static void main(String args[])
	{
		String converterChoice;
 
		int i = 0;
		// counter for loop
		while (i < 1)
		// loop continues until the user enters valid information
		{
 
			converterChoice = JOptionPane.showInputDialog("Would you like to convert English or Metric distance: ");
	 		if (converterChoice.equals("Metric"))
				 metricCoverter();
			else if (converterChoice.equals("English"))
				englishConverter();
			else JOptionPane.showMessageDialog(null, "Your Entry is invalid, please retry", "Error", JOptionPane.INFORMATION_MESSAGE);
		}
	}
	public static void metricCoverter()
	{
		String metricEntry;
		double metricDouble;
		double conversion;
 
		metricEntry = JOptionPane.showInputDialog("Enter the number of kilometers to be converted to miles: ");
		//create a double from the string
		metricDouble = Double.parseDouble(metricEntry);
		//convert to kilometers
		conversion = metricDouble * .62;
		JOptionPane.showMessageDialog(null, "Your entry of " + metricEntry + "miles converts to " + conversion + "kilomters", "Conversion to Kilometers", JOptionPane.INFORMATION_MESSAGE);
	}
	public static void englishConverter()
	{
		String englishEntry;
		double englishDouble;
		double conversion;
 
		englishEntry = JOptionPane.showInputDialog("Enter the number of miles to be converted to kilometers: ");
		//create a double from the string
		englishDouble = Double.parseDouble(englishEntry);
		//convert to miles
		conversion = englishDouble * 1.609344;
		JOptionPane.showMessageDialog(null, "Your entry of " + englishEntry + "kilometers converts to " + conversion + "miles", "Conversion to Miles", JOptionPane.INFORMATION_MESSAGE);
	}
}

[/highlight]
Can anyone give me a hint on this one?
Thanks

When posting code, make sure you use the code tags. Nobody likes to read unformatted code.

There are a few different way to do this. You could read the values in as Strings, then make sure each character is a digit before converting (see the API for String and Character for useful functions), or you could catch the Exception thrown when you try to convert a non-numeric String into a number.

try/catch statements. I'm sort of in the middle of something, so I can't really go too indepth. Basically, before you read in the number the user inputs, put a try statement. At the end of whatever segment of code you are working with, add a catch(Exception ex){...} statement. Then assume the user will input a number. If there is a problem with converting the user's input into a number, an exception will be thrown which is caught by the catch statement, where you have specified what to do in the event of an exception being thrown.

I'll post some code later if no one beats me to it.

int i =0;
 
while (i < 1)
		// loop continues until the user enters valid information
		{
 
			converterChoice = JOptionPane.showInputDialog("Would you like to convert English or Metric distance: ");
	 		if (converterChoice.equals("Metric"))
				 metricCoverter();
			else if (converterChoice.equals("English"))
				englishConverter();
			else JOptionPane.showMessageDialog(null, "Your Entry is invalid, please retry", "Error", JOptionPane.INFORMATION_MESSAGE);
		}

That's an infinite loop.

Also, for English or Metric, are you allowed to have buttons instead?

JFrame frame = new JFrame();
 
Object[] options = {"English", "Metric"};
                    int n = JOptionPane.showOptionDialog(frame,
                                    "Message",
                                    "Title",
                                    JOptionPane.YES_NO_OPTION,
                                    JOptionPane.QUESTION_MESSAGE,
                                    null,
                                    options,
                                    options[0]);
if (n == JOptionPane.YES_OPTION)
{
 
// stuff for English system
 
}
 
else if (n== JOptionPane.NO_OPTION)
{
// Metric System
}
 
else if (n== JOptionPane.CLOSED_OPTION)
{
// exit or do something if they just exit the dialog
}
 
else
{
System.out.println("Error");
}

Also, for the error checking, have a while loop that has a boolean set to false and will continue while boolean is false.

Define value you're using before while loop and catch block. Or at least initialize them.

Then have a try block that has the user enter the stuff in a JOptionPane.

At the end, before the ending bracket of try block, set boolean to true.

Then create a catch block

catch(NumberFormatException nfeRef)
{
// what to pop up if value is wrong type
valueEntered = 0; // I think it has to reset value again so it won't go on forever, could be mistaken.  
}

If there is an error, it'll go to the catch block , if not, it'll set condition to true and end while loop.