Check for zero

Question

I am looking for a way to check input fields for zero values in my action listener and bring up a message dialog if it finds one. I can get it to look for null or alpha characters but I can't figure out how to look for zero. Any suggestion would be appreciated. My action listener code is below...
public class MyActionListener1 implements ActionListener
    double newAmount;
    double newRate;
    double newTerm;
    // Tell the JButton (calcButton) what to do when clicked.
    public void actionPerformed(ActionEvent evt)
        try
            AbstractButton calcButton = (AbstractButton)evt.getSource();
            newAmount = Double.parseDouble(principleValueText.getText());
            newRate = Double.parseDouble(rateAPRText.getText());
            newTerm = Double.parseDouble(termYearsText.getText());
            pmtText.setText(nf.format(getMortgagePmt(newAmount, newTerm, newRate)));
            pmtText.setForeground(Color.red);
            principleValueText.setText(nf.format(newAmount));
            rateAPRText.setText(np.format(newRate/100));
            termYearsText.setText(ni.format(newTerm));
        // Privide error handeling to check for valid input.
        catch(NumberFormatException nfe)
            JOptionPane.showMessageDialog(null, "The value must only contain digits",
                                                      "Input Error", JOptionPane.WARNING_MESSAGE);
}

Answer 1

I don't quite understand your problem, but I think what you're saying is that if any of the parsed numbers are 0, you want to show a dialog box that says you can't have "0" values?
There are two ways to do this: after parsing each number, you can just simply use the block:
if(number == 0){
    JOptionPane.showMessageDialog(null,"...","...",...);
}You can call the JOptionPane methods whenever you want to in your program.
Now, another way of doing this, though kind of like over kill, you can use a block like this:
if(number == 0)
    throw new IllegalArgumentException("Number cannot be 0!");and then after your catch(NumberFormatException) block put:
catch(IllegalArgumentException iae){
    JOptionPane.showMessageDialog(null,iae.getCause(),"Error",JOptionPane.ERROR_MESSAGE);
}or something to that effect. once again, second solution is kind of overkill, but it would work (and stop the execution of the rest of the method)
If I completely understood your problem, I'm sorry =D
Alex