Java - Program which remembers/saves entered fields

Question

I have a program that uses three JTextField fields as the main data entry fields. I want to have it so that when the user terminates the program and then opens it again, their last entry will still be in the fields.

How could I achieve this? Would I need some sort of database or is there a simpler way?

Answer 1

the simplest way to achieve this is to add a listener to the text field and use the java preferences api:

textField = new JTextField();
    // set document listener
    textField.getDocument().addDocumentListener(new MyListener());
    // get the preferences associated with your application
    Preferences prefs = Preferences.userRoot().node("unique_string_representing_your_preferences");
    // load previous value
    textField.setText(prefs.get("your_preference_unique_key", ""));

class MyListener implements DocumentListener {

    @Override
    public void changedUpdate(DocumentEvent event) {
        final Document document = event.getDocument();
        // get the preferences associated with your application
        Preferences prefs = Preferences.userRoot().node("unique_string_representing_your_preferences");
        try {
            // save textfield value in the preferences object
            prefs.put("your_preference_unique_key", document.getText(0, document.getLength()));
        } catch (BadLocationException e) {
            e.printStackTrace();
        }
    }

    @Override
    public void insertUpdate(DocumentEvent arg0) {
    }

    @Override
    public void removeUpdate(DocumentEvent arg0) {
    }
}

but in this way every time you change value in the text field it is saved. If you want to save it only when application is closed, you can add a WindowListener to your application and write in its

windowClosing

method the content of the previous changedUpdate.