Area Calculator not working and not sure why

Question

This is the source code for my calculator that i am building in eclipse windowbuilder, i am trying to make two textFields read input and output the area for a simple rectangle, i can type the numbers into the boxes however the numbers do not compute and i am at a loss as to what i could be doing wrong, please critique my code and let me know why it isn't working. Thank you

*Edit, i have removed and changed a few things and now the Answer box displays 0.0 and nothing else

    import java.awt.EventQueue;


public class GUI {

private JFrame frame;
private JTextField textField;
private JTextField textField_1;
private JTextField textField_2;

/**
 * Launch the application.
 */
public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                GUI window = new GUI();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public GUI() {
    initialize();
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 694, 499);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    JTabbedPane tabbedPane = new JTabbedPane(JTabbedPane.TOP);
    frame.getContentPane().add(tabbedPane, BorderLayout.CENTER);

    JPanel panel = new JPanel();
    tabbedPane.addTab("New tab", null, panel, null);
    panel.setLayout(null);

    JLabel lblInputBase = new JLabel("Input Base");
    lblInputBase.setBounds(0, 0, 57, 39);
    panel.add(lblInputBase);

    textField = new JTextField();
    textField.setBounds(0, 28, 86, 20);
    panel.add(textField);
    textField.setColumns(10);
    double value = Double.parseDouble(textField.getText());
    JLabel lblInputHeight = new JLabel("Input Height");
    lblInputHeight.setBounds(0, 212, 68, 20);
    panel.add(lblInputHeight);


    textField_1 = new JTextField();
    textField_1.setBounds(0, 230, 86, 20);
    panel.add(textField_1);
    textField_1.setColumns(10);
    double value_1 = Double.parseDouble(textField_1.getText());

    double Area = value*value_1;
    String finalArea = Double.toString(Area);

    JLabel lblArea = new JLabel("Area:");
    lblArea.setBounds(244, 119, 75, 68);
    panel.add(lblArea);

    textField_2 = new JTextField();
    textField_2.setBounds(273, 143, 86, 20);
    panel.add(textField_2);
    textField_2.setColumns(10);
    textField_2.setEditable(false);
    textField_2.setText(finalArea);

    }
}

Answer 1

Your code is really confusing, but here are some problems that I found:

double value = Double.parseDouble(textField.getText());

This is being run before the user has any chance to even look at the gui. textField.getText() will return an empty string here, and the parseDouble method will always throw a NumberFormatException when the program is run, as it does not consider an empty string to be a valid number format.

double Area = Double.parseDouble(value)*Double.parseDouble(value_1);

Here, the variable value is already a double and does not need to be parsed, and the variable value_1 doesn't exist.

Where you meant to assign an actionListener to textField_1, you assigned a second one to textField.

Overall, it seems that all your calculation logic is being run in your initialize() method, and this means that it is only being run once. You'll want your math to be run whenever one of the text fields is updated.

Your field names are horribly confusing. Your textField variable names should give some indication of their function, like areaTextField, baseTextField, heightTextField.

---

Here is a modification of your code that seems to function as you intended yours to function. Note the addition of a calculate() method that is called by the action listeners that will find the area and display it, or display NaN (Not a Number) if either of the input fields are not valid numbers. All of your GUI code is retained as is, excepting the renaming of the text field variables.

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTabbedPane;
import javax.swing.JTextField;

public class GUI {
    private JFrame frame;
    private JTextField baseTextField;
    private JTextField heightTextField;
    private JTextField areaTextField;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    GUI window = new GUI();
                    window.frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the application.
     */
    public GUI() {
        initialize();
    }

    /**
     * Initialize the contents of the frame.
     */
    private void initialize() {
        frame = new JFrame();
        frame.setBounds(100, 100, 694, 499);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JTabbedPane tabbedPane = new JTabbedPane(JTabbedPane.TOP);
        frame.getContentPane().add(tabbedPane, BorderLayout.CENTER);

        JPanel panel = new JPanel();
        tabbedPane.addTab("New tab", null, panel, null);
        panel.setLayout(null);

        JLabel lblInputBase = new JLabel("Input Base");
        lblInputBase.setBounds(0, 0, 57, 39);
        panel.add(lblInputBase);

        baseTextField = new JTextField();
        baseTextField.setBounds(0, 28, 86, 20);
        panel.add(baseTextField);
        baseTextField.setColumns(20);
        baseTextField.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                calculate();
            }
        });

        JLabel lblInputHeight = new JLabel("Input Height");
        lblInputHeight.setBounds(0, 212, 68, 20);
        panel.add(lblInputHeight);

        heightTextField = new JTextField();
        heightTextField.setBounds(0, 230, 86, 20);
        panel.add(heightTextField);
        heightTextField.setColumns(20);
        heightTextField.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                calculate();
            }
        });

        JLabel lblArea = new JLabel("Area:");
        lblArea.setBounds(244, 119, 75, 68);
        panel.add(lblArea);

        areaTextField = new JTextField();
        areaTextField.setBounds(273, 143, 86, 20);
        panel.add(areaTextField);
        areaTextField.setColumns(20);
        areaTextField.setEditable(false);
    }

    private void calculate() {
        try {
            double base = Double.parseDouble(baseTextField.getText());
            double height = Double.parseDouble(heightTextField.getText());
            double area = base * height;
            areaTextField.setText(String.format("%.4f", area));
        } catch (NumberFormatException e) {
            areaTextField.setText("NaN");
        }
    }
}

Note that you need to hit the enter key in one of the two fields to update the area field. That is what it takes to trigger the ActionListener for a JTextField.