Is it possible to calculate JTextFields into a JLabel as they are being typed?

Question

Is it possible to calculate a group of JTextFields as they are typed in and set the result to a JLabel?

For Example:

int iCalc = 0;
JTextField x = new JTextField();
JTextField y = new JTextField();
JTextField z = new JTextField();

JLabel lCalc = new JLabel("Your total is: " + calc);

As i am typing, calc gets calculated. I put in x "12" and 12 is shown. and in y i put "10" 22 is automatically typed in.. ect, ect.

To clarify "automatically" i don't want to use key listener (like pressing tab to for next TextField) (unless it is absolutely necessary) And I don't want to hit a button to do the calculations

Its much like typing Hello World into a String: as I Type the Label will show: "H", "e", "l" ect, ect.

Hope I clarified enough

Yes, a computer is completely able to be programmed to do such things. — Brian Roach, Aug 10 '13 at 19:26
For entering integers, use a `JSpinner`. The `ChangeListener` can invoke the addition. — Andrew Thompson, Aug 10 '13 at 19:50
When you do this also make sure you don't do it in the `EDT` I can already see a "why does my `GUI` freeze" question coming... — 0x6C38, Aug 10 '13 at 23:59

score 4 · Accepted Answer · edited May 23 '17 at 11:58

You can use a DocumentListener for this purpose, add it to the Document of each JTextField in question and perform the addition operation in the insertUpdate(...) and removeUpdate(...) method of the DocumentListener interface.

Here is one working example, for further insight :

import java.awt.*;
import javax.swing.*;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;

public class DocumentListenerExample {

    private JPanel contentPane;
    private JPanel compPanel;
    private JTextField firstField;
    private JTextField secondField;
    private JTextField thirdField;
    private JLabel resultLabel;

    private static final String RESULT = "Result : ";
    private int result;

    private void displayGUI() {
        JFrame frame = new JFrame("Document Listener Example");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        contentPane = new JPanel(new GridBagLayout());
        compPanel = new JPanel(new BorderLayout(5, 5));

        JPanel fieldPanel = new JPanel(new GridLayout(3, 3, 5, 5));
        JLabel firstLabel = new JLabel("First Number : ", JLabel.CENTER);
        firstField = new JTextField(10);
        firstField.getDocument().addDocumentListener(
                                    new MyDocumentListener());
        JLabel secondLabel = new JLabel("Second Number : ", JLabel.CENTER);
        secondField = new JTextField(10);
        secondField.getDocument().addDocumentListener(
                                    new MyDocumentListener());
        JLabel thirdLabel = new JLabel("Third Number : ", JLabel.CENTER);
        thirdField = new JTextField(10);
        thirdField.getDocument().addDocumentListener(
                                    new MyDocumentListener());
        fieldPanel.add(firstLabel);
        fieldPanel.add(firstField);
        fieldPanel.add(secondLabel);
        fieldPanel.add(secondField);
        fieldPanel.add(thirdLabel);
        fieldPanel.add(thirdField);

        JPanel footerPanel = new JPanel();
        resultLabel = new JLabel((RESULT + "0"), JLabel.CENTER);
        footerPanel.add(resultLabel);

        compPanel.add(fieldPanel, BorderLayout.CENTER);
        compPanel.add(footerPanel, BorderLayout.PAGE_END);
        contentPane.add(compPanel);

        frame.setContentPane(contentPane);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private class MyDocumentListener implements DocumentListener {

        @Override
        public void changedUpdate(DocumentEvent de) {}

        @Override
        public void insertUpdate(DocumentEvent de) {
            calculateSum();
        }

        @Override
        public void removeUpdate(DocumentEvent de) {
            calculateSum();
        }

        private void calculateSum() {
            int first = 0, second = 0, third = 0;
            if (firstField.getDocument().getLength() > 0)
                first = Integer.parseInt(firstField.getText()); 
            if (secondField.getDocument().getLength() > 0)
                second = Integer.parseInt(secondField.getText());
            if (thirdField.getDocument().getLength() > 0)
                third = Integer.parseInt(thirdField.getText());
            result = first + second + third;
            resultLabel.setText(RESULT + result);
        }
    }

    public static void main(String[] args) {
        Runnable runnable = new Runnable() {
            @Override
            public void run() {
                new DocumentListenerExample().displayGUI();
            }
        };
        EventQueue.invokeLater(runnable);
    }
}

You might have to add a DocumentFilter too to the Document to only allow putting Digit inside the JTextField, instead of any random character. Here is a related example

@kleopatra : Thankyou for pointing out :-) I missed the part, if the user enters a backspace to cancel the update :(. Now corrected :-) — nIcE cOw, Aug 11 '13 at 10:23
@kleopatra : The best I can think of right now, is that I can make a simple function, and call this function, instead of rewriting it again. I hope you meant exactly this, or else I would be on my way to learn something new today :-) — nIcE cOw, Aug 11 '13 at 11:31

score 1 · Answer 2 · answered Aug 10 '13 at 19:27

1

You need to read about listeners in the java tutorial and implement a listner that will convert the strings typed into numbers, and then update the label's text.

answered Aug 10 '13 at 19:27

Dodd10x

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Is it possible to calculate JTextFields into a JLabel as they are being typed?

2 Answers2

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