Returns the amount to change the scrollbar's value by, given a unit up/down request. A ScrollBarUI implementation typically calls this method when the user clicks on a scrollbar up/down arrow and uses the result to update the scrollbar's value. Subclasses my override this method to compute a value, e.g. the change required to scroll up or down one (variable height) line text or one row in a table.
The JScrollPane component creates scrollbars (by default) that override this method and delegate to the viewports Scrollable view, if it has one. The Scrollable interface provides a more specialized version of this method.
Some look and feels implement custom scrolling behavior and ignore this property.
direction | is -1 or 1 for up/down respectively |
setUnitIncrement, setValue, Scrollable.getScrollableUnitIncrement
Diagram: Scrolling