Learning Java, 4th Edition

The JScrollPane Class

We used JScrollPane earlier in this chapter without explaining much about it. In this section, we’ll remedy the situation.

A JScrollPane is a container that can hold one component. Said another way, a JScrollPanewraps another component. By default, if the wrapped component is larger than the JScrollPane itself, the JScrollPane supplies scrollbars. JScrollPane handles the events from the scrollbars and displays the appropriate portion of the contained component.

Technically, JScrollPane is a Container, but it’s a funny one. It has its own layout manager, which can’t be changed, and it accommodates only one component at a time. This isn’t really a limitation. If you want to put a lot of stuff in a JScrollPane, just collect your components in a JPanel, with whatever layout manager you like, and put that panel into the JScrollPane.

When you create a JScrollPane, you specify the conditions under which its scrollbars are displayed. This is called the scrollbar display policy; a separate policy is used for the horizontal and vertical scrollbars. The following constants can be used to specify the policy for each of the scrollbars:

HORIZONTAL_SCROLLBAR_AS_NEEDEDVERTICAL_SCROLLBAR_AS_NEEDED

Displays a scrollbar only if the wrapped component doesn’t fit.

HORIZONTAL_SCROLLBAR_ALWAYSVERTICAL_SCROLLBAR_ALWAYS

Always shows a scrollbar, regardless of the contained component’s size.

HORIZONTAL_SCROLLBAR_NEVERVERTICAL_SCROLLBAR_NEVER

Never shows a scrollbar, even if the contained component ...