Scrollbars come in two flavors: horizontal and vertical. It's not clear whether this is appropriate behavior or a bug (remember, an interface only lists methods that must be present but doesn't require them to do anything) it may change in a later release. You can't change the settings or register AdjustmentListeners the appropriate methods exist, but they don't do anything. Currently, you can use the ScrollPane's “adjustables” to find out the scrollbar settings in each direction. The Scrollbar class implements Adjustable a ScrollPane has two methods that return an Adjustable object, one for each scrollbar. Adjustable defines the common scrolling activities of the two classes.
VOLUME SCROLL BAR DRIFTS TO THE RIGHT HOW TO
This saves you the burden of implementing scrolling yourself: generating scrollbars, handling their events, and figuring out how to redisplay the screen accordingly.īoth Scrollbar and ScrollPane take advantage of the Adjustable interface. You could use a ScrollPane to implement a drawing pad that could cover an arbitrarily large area. In this sense, it's like TextArea, which contains its own scrollbars. A ScrollPane is like a Panel, but it has scrollbars and scrolling built in.
Release 1.1 of AWT also includes a ScrollPane container object it is a response to one of the limitations of AWT 1.0. With Java 1.1, you handle scrolling events by registering an AdjustmentListener with the Scrollbar.addAdjustmentListener() method when adjustment events occur, the listener's adjustmentValueChanged() method is called. To work with them, you must override the handleEvent() method.
In Java 1.0, none of these events trigger a default event handler like the action() method. Unlike other components, which generate an ACTION_EVENT when something exciting happens, the Scrollbar generates five events: SCROLL_LINE_UP, SCROLL_LINE_DOWN, SCROLL_PAGE_UP, SCROLL_PAGE_DOWN, and SCROLL_ABSOLUTE. The Scrollbar reports scrolling actions through the standard event mechanisms it is up to the programmer to handle those events and perform the scrolling. Anything else is your responsibility: if you want to display the value of the setting (for example, if you're using the scrollbar as a volume control) or want to change the display (if you're using scrollbars to control an area that's too large to display), you have to do it yourself. It really provides only the means to read a value from a slider setting. The first is the fairly primitive Scrollbar object. This chapter describes how Java deals with scrolling.
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