101

Java JViewport

The JViewport class is used to implement scrolling. JViewport is designed to support both logical scrolling and pixel-based scrolling. The viewport’s child, called the view, is scrolled by calling the JViewport.setViewPosition() method.

Nested Classes

Modifier and Type	Class	Description
protected class	JViewport.AccessibleJViewport	This class implements accessibility support for the Jviewport class.
protected class	JViewport.ViewListener	A listener for the view.

Fields

Modifier and Type	Field	Description
static int	BACKINGSTORE_SCROLL_MODE	It draws viewport contents into an offscreen image.
protected Image	backingStoreImage	The view image used for a backing store.
static int	BLIT_SCROLL_MODE	It uses graphics.copyArea to implement scrolling.
protected boolean	isViewSizeSet	True when the viewport dimensions have been determined.
protected Point	lastPaintPosition	The last viewPosition that we’ve painted, so we know how much of the backing store image is valid.
protected boolean	scrollUnderway	The scrollUnderway flag is used for components like JList.
static int	SIMPLE_SCROLL_MODE	This mode uses the very simple method of redrawing the entire contents of the scrollpane each time it is scrolled.

Constructor

Constructor	Description
JViewport()	Creates a JViewport.

Methods

Modifier and Type	Method	Description
void	addChangeListener(ChangeListener l)	It adds a ChangeListener to the list that is notified each time the view’s size, position, or the viewport’s extent size has changed.
protected LayoutManager	createLayoutManager()	Subclassers can override this to install a different layout manager (or null) in the constructor.
protected Jviewport.ViewListener	createViewListener()	It creates a listener for the view.
int	getScrollMode()	It returns the current scrolling mode.
Component	getView()	It returns the JViewport’s one child or null.
Point	getViewPosition()	It returns the view coordinates that appear in the upper left hand corner of the viewport, or 0,0 if there’s no view.
Dimension	getViewSize()	If the view’s size hasn’t been explicitly set, return the preferred size, otherwise return the view’s current size.
void	setExtentSize(Dimension newExtent)	It sets the size of the visible part of the view using view coordinates.
void	setScrollMode(int mode)	It used to control the method of scrolling the viewport contents.
void	setViewSize(Dimension newSize)	It sets the size of the view.

---

JViewport Example

Output: