Question

When writing a graphical interface, using Java, what’s the appropriate way of switching between the different windows of the application, when clicking a button for example? I.E. what are the windows supposed to be, JPanels, JFrames…? And how do all the components ‘see’ the ‘domain controller’ (the class that links the graphical package to the application logic package)?

Any guide or reference would be appreciated.

Answer 1

You start your application with your Controller. In the constructor of your controller, you are going to initialize the first GUI you want to open, lets say GUI_A:

private GUI_A gui_a = null;

Controller() {
    gui_a = new GUI_A(this);
}

As you might notice, I called the constructor of GUI_A with one parameter: this. this is referencing the instance of the current class, so this is type of Controller. The constructor of GUI_A has to look something like this:

private Controller controller = null;

GUI_A(Controller ctrl) {
    controller = ctrl;
}

This is a simple way to get the GUI known to the Controller.

The next thing you would do is displaying GUI_A:

gui_a.setVisible(true);

If you now want to handle button-clicks, you would do it like this:

First, you add the action-performed method to your button. And, as it is best practice in MVC, you don’t want to do logic in your view/GUI. So you also create a corresponding method in your Controller for the action-performed, and call it from your GUI:

// Controller
GUI_A_button1_actionPerformed(ActionEvent evt) {
    // Add your button logic here
}

// GUI_A
button1_actionPerformed(ActionEvent evt) {
    controller.GUI_A_button1_actionPerformed(evt);
}

Usually you don’t need to pass the ActionEvent-var to the Controller, as you will not need it often. More often you would read a text out of a TextField and pass it on to your Controller:

// Controller
GUI_A_button1_actionPerformed(String text) {
    // Add logic for the text here
}

// GUI_A
button1_actionPerformed(ActionEvent evt) {
    controller.GUI_A_button1_actionPerformed(textField1.getText());
}

If you now want to access some fields on your GUI_A from the Controller, be sure not to mark the fields as public in your GUI, but to create public methods which handle how to display the values.