Handling events between classes

Question

I have a main class with an Editor class (with a JTextPane) and a Toolbar class (with a JList and a Jbutton, I don't want to use JToolBar). These two classes are composed by many components and I would like not to mix them into the same class. I want the editor and the toolbar to communicate. Let's say I write "Hello" in the toolbar and then click on Submit. I want the text pane to show me "Hello". I build the classes this way:

public class Main{
    public MainGUI(){
        initComponents();
    }

    private void initComponents(){
        JFrame mainframe=new JFrame("Main Frame");
        Editor editor=new Editor();
        Toolbar toolbar=new Toolbar();
        mainframe.getContentPane().setLayout(new BorderLayout());
        mainframe.getContentPane().add(editor, BorderLayout.CENTER);
        mainframe.getContentPane().add(toolbar, BorderLayout.NORTH);
        mainframe.setVisible(true);
    }
}

public class Editor extends JPanel{
    public Editor(){
        super();
        initComponents();
    }

    private void initComponents(){
        JTextPane textpane=new JTextPane();

        this.setLayout(new BorderLayout());
        this.add(textpane, BorderLayout.CENTER);
    }
}

public class Toolbar extends JPanel{
    public Toolbar(){
        super();
        initComponents();
    }

    private void initComponents(){
        JTextField textfield=new JTextField();
        JButton submitbutton=new JButton("Submit");

        this.setLayout(newFlowLayout());
        this.add(textfield);
        this.add(submitbutton);
    }
}

How should I implement the event handling betweenthe Toolbar and the Editor?

Answer 1

You can create an interface ValueSubmittedListener

interface ValueSubmittedListener {
    public void onSubmitted(String value);
}

and have Editor implements it.

class Editor implements ValueSubmittedListener{

    ...

    public void onSubmitted(String value) {
        // add text to JTextPane.
    }
}

Then have Toolbar provide methods

class Toolbar {

    private List<ValueSubmittedListener> listeners = new ArrayList<ValueSubmittedListener>();


    public void addListener(ValueSubmittedListener listener) {
        listeners.add(listener);
    }

    private void notifyListeners() {
        for (ValueSubmittedListener listener : listeners) {
            listener.onSubmitted(textfield.getText());
        }
    }

}

Then everytime you need to send new value to Editor (i.e: in submitButton's ActionListener), just invoke the method notifyListeners.

UPDATE:

I forgot to mention that in the initComponents of Main, you have to register Editor to Toolbar:

private void initComponents() {
   JFrame mainframe = new JFrame("Main Frame");
   Editor editor = new Editor();
   Toolbar toolbar = new Toolbar();
   toolbar.addListener(editor); // register listener
   ...
}