Difference between JScrollPane.setviewportview vs JScrollPane.add

Question

I faced this new thing today, and I didn't know why. When I want to show something in panel for example, I just add it to panel; but why I cannot add a table to scroll pane directly, and why I have to call the setviewportview() method? What does add() method do and what does setViewProtView() do?

Reneerenegade

Answer 1

Basically, you should not use JScrollPane#add.

JScrollPane has a single component already attached to it, a JViewport, this is what the JScrollPane uses to display any component added to the view port.

setViewportView is a convenience method for for JScrollPane#getViewport#setView

The basic concept comes down to the fact that from the scroll panes point of view, it will only show a single component, so add doesn't actually make any sense for it. The method is a consequence of extending from JComponent -> Container

Mimesis

Great answer. I found several answers pointing to use setViewPortView, but no one explained like you did here - 1. basically JScrollpane already has a component called Viewport, 2. add is just redundant method came through inheritance! Thanks for explaining it nicely. – Chandler

Why couldn't JScrollPane#add be overridden to behave as expected? – Jewelfish

@Jewelfish You'd have to ask the original framework developers, but, add comes from java.awt.Container, so it's inheritance issue – Mimesis