FIGURE 24-5
Sample output from the ListDemo applet
Managing Scroll Bars
Scroll bars are used to select continuous values between a specified minimum and maximum.
Scroll bars may be oriented horizontally or vertically. A scroll bar is actually a composite of
several individual parts. Each end has an arrow that you can click to move the current value
of the scroll bar one unit in the direction of the arrow. The current value of the scroll bar
relative to its minimum and maximum values is indicated by the slider box (or thumb) for the
scroll bar. The slider box can be dragged by the user to a new position. The scroll bar will
then reflect this value. In the background space on either side of the thumb, the user can
click to cause the thumb to jump in that direction by some increment larger than 1. Typically,
this action translates into some form of page up and page down. Scroll bars are encapsulated
by the Scrollbar class.
Scrollbar defines the following constructors:
Scrollbar( ) throws HeadlessException
Scrollbar(int style) throws HeadlessException
Scrollbar(int style, int initialValue, int thumbSize, int min, int max)
throws HeadlessException
The first form creates a vertical scroll bar. The second and third forms allow you to specify
the orientation of the scroll bar. If style is Scrollbar.VERTICAL, a vertical scroll bar is created.
If style is Scrollbar.HORIZONTAL, the scroll bar is horizontal. In the third form of the
constructor, the initial value of the scroll bar is passed in initialValue. The number of units
represented by the height of the thumb is passed in thumbSize. The minimum and maximum
values for the scroll bar are specified by min and max.
If you construct a scroll bar by using one of the first two constructors, then you need to
set its parameters by using setValues( ), shown here, before it can be used:
void setValues(int initialValue, int thumbSize, int min, int max)
The parameters have the same meaning as they have in the third constructor just described.
To obtain the current value of the scroll bar, call getValue( ). It returns the current
setting. To set the current value, call setValue( ). These methods are as follows:
int getValue( )
void setValue(int newValue)
Search WWH :
