CardLayout doesn't show JButtons when I add static to arraylist with JButtons

Question

I don't know what is wrong, but it's very interesting. I made code with CardLayout and panels. On panel with CardLayout I put JButtons from ArrayList and it is working...

It's looking like this:

Panel with CardLayout is on the bottom with pink JButtons.....part of my code is

public class Controller extends JPanel {

ArrayList<JButton> tnp=new ArrayList<JButton>();
ArrayList<JButton> sokp=new ArrayList<JButton>();
ArrayList<JButton> alkp=new ArrayList<JButton>();


CardLayout cardlayout=new CardLayout();
JPanel cardpanel = new JPanel(cardlayout);

but, when I add static to ArrayList like this:

static ArrayList<JButton> tnp=new ArrayList<JButton>();
static ArrayList<JButton> sokp=new ArrayList<JButton>();
static ArrayList<JButton> alkp=new ArrayList<JButton>();

my applicaton look like this:

As you can see, program still shows panel with CardLayout, (border with red ) but JButtons from

static ArrayList<JButton> tnp=new ArrayList<JButton>();
static ArrayList<JButton> sokp=new ArrayList<JButton>();
static ArrayList<JButton> alkp=new ArrayList<JButton>();

lost! why?

I don't unerstand. One ArrayList is for one panel with cardlayout, that panel is for all JTabbedPane, and I want to have access to that list from another class (that is why I want to be static), to add or remove buttons to that panel. But I can't, nothing adds to that arraylist .

Answer 1

A static field is a field that belongs to the class it's declared in. Whereas an instance (non-static) field belongs to an instance of the class it's declared in.

So, if you have the following:

public class Controller {
    public static List<JButton> staticList = new ArrayList<JButton>();
    public List<JButton> instanceList = new ArrayList<JButton>();

    ...
}

and the following user code:

Controller c1 = new Controller();
Controller c2 = new Controller();

each controller has its own instance list, but they both share a unique static list.

You want every controller to have its own buttons, so you definitely don't want static lists.

If you want to have access to a controller from another object, you simply need to pass the controller to this other class instance:

Controller c1 = new Controller();
OtherClass other = new OtherClass(c1);

And inside OtherClass, you can do whatever you want with the controller:

private Controller theController;

public OtherClass(Controller controller) {
    this.theController = theController;
}

public void foo() {
    // call any method you want from theController
}