Learning Java

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 JScrollPane wraps 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. It can accommodate only one component at a time. This seems like a big limitation, but it isn’t. If you want to put a lot of stuff in a JScrollPane, just put your components into a JPanel, with whatever layout manager you like, and put that panel into the JScrollPane.

When you create a JScrollPane, you can specify the conditions under which its scrollbars will be 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_NEEDED

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

HORIZONTAL_SCROLLBAR_ALWAYS

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

HORIZONTAL_SCROLLBAR_NEVER

Never shows a scrollbar, even if the contained component won’t fit. If you use this policy, you ...