JFrame, JTextArea, and Setting Variables

Question

I have a program that I want to use a JFrame and 8 text areas to set the values of 8 variables. When I fill in all of the text areas, the program runs. When I leave a text area blank the program fails. I get the following error:

Exception in thread "AWT-EventQueue-0" java.lang.NumberFormatException: empty String

Then I get a long list of what I think are the locations the error occurred?

So I tried to use this if statement to say that if the text areas that set the values of x3,y3,x4,y4 were left blank, the program would still run.

I have parts of the program that will handle just having 2, 3, and 4 coordinate pairs respectively.

if(x3 == null && y3 == null && x4 == null && y4 == null){
r1 = new Regression(x1,y1,x2,y2,x3,y3,x4,y4);
r1.computation();
}

Under x3 == null and the others I get: The operator == is undefined for the argument type(s) double, null

Any ideas on how I can get the program to run without having all of the text areas filled?

I'm new to Java and I'm just beginning to get comfortable with it.

EDIT: Full Code Below

    package javaPackage;

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;


public class Frame extends JFrame {

    private static final long serialVersionUID = 1L;
    public double x1;
    public double y1;
    public double x2;
    public double y2;
    public double x3;
    public double y3;
    public double x4;
    public double y4;


    public Regression r1;
    public Regression2 r2;

    public static void main(String[] args){
        new Frame().setVisible(true);
    }

    public Frame(){

        super("Senior Design");
        setSize(600, 600);
        setResizable(false);
        setDefaultCloseOperation(EXIT_ON_CLOSE);
        setLayout(new FlowLayout());



        final JTextArea x1Test= new JTextArea (1,1);
        final JTextArea y1Test= new JTextArea (1,1);
        final JTextArea x2Test= new JTextArea (1,1);
        final JTextArea y2Test= new JTextArea (1,1);
        final JTextArea x3Test= new JTextArea (1,1);
        final JTextArea y3Test= new JTextArea (1,1);
        final JTextArea x4Test= new JTextArea (1,1);
        final JTextArea y4Test= new JTextArea (1,1);
        add(x1Test);
        add(y1Test);
        add(x2Test);
        add(y2Test);
        add(x3Test);
        add(y3Test);
        add(x4Test);
        add(y4Test);

        JButton button = new JButton("Compute");
        add(button);
        button.addActionListener(new ActionListener(){

            @Override
            public void actionPerformed(ActionEvent arg0) {
                // TODO Auto-generated method stub
                x1 = Double.parseDouble(x1Test.getText()); //need to convert to doubles
                y1 = Double.parseDouble(y1Test.getText());
                x2 = Double.parseDouble(x2Test.getText());
                y2 = Double.parseDouble(y2Test.getText());
                x3 = Double.parseDouble(x3Test.getText());
                y3 = Double.parseDouble(y3Test.getText());
                x4 = Double.parseDouble(x4Test.getText());
                y4 = Double.parseDouble(y4Test.getText());


                if(x3 == null && y3 == null && x4 == null && y4 == null){
                r1 = new Regression(x1,y1,x2,y2,x3,y3,x4,y4);
                r1.computation();
                }


                r2=new Regression2(x1,y1,x2,y2,x3,y3,x4,y4);//initializes the variables
                r2.computation();//starts the computation


            }
        });


    }
    }

primitives can't be null. numeric primitives are defaulted with 0, not null — Paul Samsotha, Apr 04 '14 at 03:17
if you can post your code it would be easy for us to find the solution. — Ashish, Apr 04 '14 at 03:18
You didn´t show us where the textareas are filed and it´s essential part of this problem. Please, show us. — Zini, Apr 04 '14 at 03:28
1) For better help sooner, post an [MCVE](http://stackoverflow.com/help/mcve) (Minimal Complete and Verifiable Example). 2) But as general tips. Don't use `JTextArea` for single line entry, instead use a `JTextField`. But better than `JTextField` for numbers, is a `JSpinner` using a `SpinnerNumberModel`. E.G. as seen [here](http://stackoverflow.com/a/10021773/418556). — Andrew Thompson, Apr 04 '14 at 04:03

Paul Samsotha · Accepted Answer · 2014-04-04T03:33:18.103

0

NumberFormatException / "Any ideas on how I can get the program to run without having all of the text areas filled?"

You're probably trying to parse the text (during initialization) before any event has been fired. It's a mistake I see a lot here. Like

JTextField field = new JTextField();
double num = Double.parseDouble(field.getText());

That's will undoubtedly get you a NumberFormatException as there is not text (empty String as the error says).

You need to wait until some event is fired before you want to parse the text, not during initialization. Like for example a button press

private double num;
private JTextField field = new JTextField();
private JButton button  = new JButton("Nutton");

...
button.addActionListener(new ActionListener(){
    public void actionPerformed(ActionEvent e) {
        num = Double.parseDouble(field.getText());
    }
});

"Under x3 == null and the others I get: The operator == is undefined for the argument type(s) double, null"

It makes sense, if x3 is a double. As I stated i my comment, primitives (int, double, etc) can't be null. They are defaulted at 0, If you want to check if they haven't been initialized, then check them against 0, not null

edited Apr 04 '14 at 03:33

answered Apr 04 '14 at 03:28

Paul Samsotha

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Ahhh now I see why I needed to include more. I've added the full code above. – William From Detroit Apr 04 '14 at 12:13
Do you not understand something about the second part of my answer? I still see you comparing doubles to null. ie `if (x3 == 0 &&` – Paul Samsotha Apr 04 '14 at 12:18
Also, you you are going to try and parse every field, then _no_ field can be empty when you press the button. Or else you _will_ get a `NumberFormatException` for the fields that are empty – Paul Samsotha Apr 04 '14 at 12:21
If you want some fields to be able to be empty, then you need to do some checks, in your actionPerformed before you try and parse them. – Paul Samsotha Apr 04 '14 at 12:24
so in action performed I would have an `if()` statement to check if there is anything in each of those fields, and then if there is, I parse only those variables? – William From Detroit Apr 04 '14 at 12:50
Something like that. Try it out. – Paul Samsotha Apr 04 '14 at 12:51
If I continue in this form (if it looks correct) what would I add to the body of the if statement? ` if(x1Test.getText().equals("")){ }else{ x1 = Double.parseDouble(x1Test.getText()); if(y1Test.getText().equals("")){ }` – William From Detroit Apr 04 '14 at 12:55
You don't need to add anything. You really don't even need an else. `if (!x1Test.getText().isEmpty()) { parse }`. If the the text is not empty then parse. No need for else – Paul Samsotha Apr 04 '14 at 12:58
Ohh that makes a lot of sense! Thanks! @peeskillet – William From Detroit Apr 04 '14 at 13:01

JFrame, JTextArea, and Setting Variables

1 Answers1