Simple GUI using tabs to separate application windows

Question

I'm designing a simple GUI using tabs to separate each 'window' of the application. There are 3 main tabs, each with 2 sub-tabs.

In one class I create the entire hierarchy of panes and panels:

mainPane = new JTabbedPane();
mainPane.setBounds(0, 0, WIDTH, HEIGHT);

//instantiate main tabs, get panes added to them
createTab = new JPanel();
createTab.setLayout(null);

customizeTab = new JPanel();
customizeTab.setLayout(null);

viewTab = new JPanel();
viewTab.setLayout(null);

//instantiate main panes, get sub-tabs added to them
createPane = new JTabbedPane();
createPane.setBounds(0, 0, WIDTH, HEIGHT);

customizePane = new JTabbedPane();
customizePane.setBounds(0, 0, WIDTH, HEIGHT);

viewPane = new JTabbedPane();
viewPane.setBounds(0, 0, WIDTH, HEIGHT);

//instantiate sub-tabs, get elements added to them
createEntityTab = new JPanel();
createEntityTab.setLayout(null);

createDealTab = new JPanel();
createDealTab.setLayout(null);

customizeEntityTab = new JPanel();
customizeEntityTab.setLayout(null);

customizeDealTab = new JPanel();
customizeDealTab.setLayout(null);

viewEntityTab = new JPanel();
viewEntityTab.setLayout(null);

viewDealTab = new JPanel();
viewDealTab.setLayout(null);

//add sub-tabs to main panes
createPane.addTab("Create Entity",null, createEntityTab);
createPane.addTab("Create Deal", null, createDealTab);

customizePane.addTab("Customize Entity", null, customizeEntityTab);
customizePane.addTab("Customize Deal", null, customizeDealTab);

viewPane.addTab("View Entity", null, viewEntityTab);
viewPane.addTab("View Deal", null, viewDealTab);

//add main panes to main tabs
createTab.add(createPane);
customizeTab.add(customizePane);
viewTab.add(viewPane);

//add main tabs to mane pane
mainPane.addTab("Create", null, createTab, "");
mainPane.addTab("Customize", null, customizeTab, "");
mainPane.addTab("View", null, viewTab, "");

and now to add elements to each sub-tab, I would like to do something like this:

new CreateEntity(createEntityTab);
new CreateDeal(createDealTab);

i.e., passing the "sub-tab" and then adding elements in the CreateEntity class.

This seems to work, but my question is the following:

Is using a constructor to pass a JPanel, and then adding elements in the new class considered bad coding?

I know using null in layout is bad practice. It's just for the question.

Answer 1

Is using a constructor to pass a JPanel, and then adding elements in the new class considered bad coding?

Not necessarily. However, if you only create an instance of the other class just to do things in the constructor, then you don't need the new class - and in that case it is considered bad coding.

If that's all you do in the constructor, then move the code from the constructor to a method (which you can place more or less anywhere, but I'd recommend having it in the original class unless you feel that the original class gets too big).

private void createEntityTab(JPanel panel) {
   ...
   panel.add(...);
   ...
}

Actually, it might be even better to let this method return the JPanel, so that you can use this code:

createPane.addTab("Create Entity", null, createEntityTab());

And use the method:

private JPanel createEntityTab() {
   JPanel panel = new JPanel();
   panel.setLayout(null);
   ...
   panel.add(...);
   ...
   return panel;
}

Answer 2

I don't see anything wrong with it. You are creating an object that is going to use that data, at construction time, to set itself up. I don't see anything objectionable if that data happens to be a UI Panel. I would think it would be (very slightly) worse to force a programmer to first use the constructor and then use a setter method to do the same thing; conceptually this links the construction with the panel, and it sounds like that fits the model you are making.