We Keep Coding

JavaFx: StageStyle.UTILITY without close button

I need to use StageStyle utility because I need to hide window icon in taskbar. However, I also need to hide and close button. How to do it? Or maybe there is another solution - no window title bar + no icon in task bar?

This answer is more of a general one: The core problem is that JavaFX doesn't allow you to hide the taskbar icon. So I guess you really don't want to use a Utility StageStyle, but rather are forced to.
Swing allows you to hide the taskbar icon. So the hackaround is simple: Use JavaFX inside a Swing JFrame and hide it from the taskbar.
You can take a look at the widget code in the answer here as an example.

New window inside a main window?

I am a beginner and I am trying to make a text editor and I want to create a pop up window for text format when I press a menu button where I can put all things like font face, font size , font style etc. Can you tell me how I can make this new window? Thanks for your patience!
For example Notepad:

I think what you're after is a dialog of some kind.
Take a look at How to Make Dialogs for more details.
What I would do is design the basic UI onto a JPanel. I would then add this JPanel to an instance of a JDialog (possibly even using a JOptionPane) and show this dialog, making sure to make it modal, so you can easily retrieve the values set by the user.
This means that you can decide how best to show the user interface or even show it in a number of different ways as it's not constrained to a single top level container

You can simply create a brand spanking new JFrame and it will still be counted as the same application.
Tip: Use Eclipse Window Builder

How to disable iconified button in Menu bar in JFrame Window?

How to disable iconified button in JFrame Window ?
something like setResizable, but for minimize button

At First, you can use the method setUndecorated(boolean). It may disable the title bar and the border.
In the end, you will create the icon label and close button at your frame top or the others position.
But this way will lose the border look and feel for the frame. If you choose this way, you must create a lot of code.
In fact, If you could not use JNI, this way may be the only.

You could use a JDialog, which natively does not have a minimize button.
In fact, the minimize, close and maximize/un-maximize buttons are drawn by the Operating System itself. This means you can't really disable them within Java.
That's why my suggestion is to use a JDialog.

Using standard buttons from a Look and Feel

I am making a UI with Swing, and I want the buttons I am using for my custom dialogs to have the same style as the ones in standard dialogs.
For instance, in the attached image I have a custom dialog and the standard file select dialog. I want the 'OK' and 'Cancel' buttons from the file select dialog to be used for the equivalent buttons in my custom dialog.
I want my application to use the default system look and feel of whatever OS it is running on, so I don't want to try to manually re-create these standard buttons. Using a more rigid Swing class that automatically provides these buttons wouldn't work either, as I'd like to also use them in other, more exotic places in my UI.
Is there an easy solution to this problem?

Sorry to be the bearer of bad news, but it look like there is no standard way to do this cross-platform. The behaviours, mnemonics and icons on default buttons are handled in very specific ways by each look-and-feel.
Here is a SO question that answers the question on how to set the default OK and Cancel buttons on a dialog (the default button is set using getRootPane().setDefaultButton(...) and the Cancel button needs a custom keyboard listener. If you're very lucky, setting the default button might add an icon to it, depending on how the UI is coded.
This forum thread addresses the issue of getting icon resources from the UIManager. Each LaF has a set of UI defaults such as colors, text, borders and icons. There are a number of default icons which are found across all LaFs, but for non-standard icons, such as ones on buttons, there are no guarantees. However, if you tell me which LaF you are using in the screenshot you provided, I can look up the resource keys used by its custom UI classes (or you can find it yourself if you have the source). You could then write a helper method which looks for the icons via these keys, and adds them to the buttons if they are found.

JButton.setUI(ButtonUI) sets the UI for just one JButton. Use that in conjunction with a factory:
public static JButton createStyledButton(String text) {
JButton button = new JButton(text);
button.setUI(STYLE_UI);
return button;
}

Adding a scrollable label to an option dialog

I am creating an options dialog using JOptionPane.showOptionDialog(...)
When I click one of the buttons added to this dialog, I need a label to apear underneath on the dialog (and this label should be scrollable if necessary). I have written event handlers for the buttons, but I am not sure how to get this label to appear on the dialog.
Any help would be great.
Update: I realized that it would be ok if I somehow called JOptionPane.showOptionDialog(...) with an initial message, and then when one of the buttons was clicked I would change the message. Is this possible?

JOptionPane static methods are only shortcuts to easily create a dialog with option buttons and a fixed message. If you check the source from it, you will see that all is wrapped in this purpose. It's only a convenience class over a frequent use case of dialogs.
The suggestion from comment is correct, if you want more than this, you will have to create your own JDialog, as it will be easier than trying to change something from this generated dialog.
Edit: You can create your own JDialog yourself, using layout managers. A more simple way, suggested as well in the previous link, is to use a GUI builder, like the one included in Netbeans.