purpose of JPanel?

Question

This write up on JPanel seems to focus on this container as a means of setting a background color. Oracle on how to use JPanel Should I infer that if I am happy with the default grey background in ubuntu/gnome/Java programs, there is no need to use this object? Is there an object-oriented programming reason to use this object?

Answer 1

JPanels are a way to create a logical "division" of space if that makes any sense. For example, if you think about HTML, you could just put elements one after another on the page (how some old HTML pages look in fact) but it's much more aesthetically pleasing to use a container like a table, or some CSS styled DIV tags to create divisions on the page, and place elements relative to one another in a much more defined manner.

JPanels fill this function in Swing, where each JPanel has a Layout Manager that defines how it's inner elements are laid out. It's not unusual to nest JPanels, for example, using a JPanel with a border layout for the menus/status bar, etc, a JPanel at the center of that with further elements, and then additional JPanels inside of that central "content panel" area that further divides the space, for example, creating an input form on one part of the central panel.

In this sense, JPanels are quite comparable to how Tables and Divs are used in HTML, and you should think of them in a similar manner when creating your layout. The most important thing about JPanels is their ability to dynamically resize, pushing the contained components around. If you just used, say, one JPanel and absolutely positioned everything, then you'd lose the main appeal of Swing, and this container methodology.