java.awt

Class Canvas

java.lang.Object

java.awt.Component

java.awt.Canvas

All Implemented Interfaces:

ImageObserver, MenuContainer, Serializable, Accessible

public class Canvas
extends Component
implements Serializable, Accessible

The Canvas component provides a blank rectangular area, which the client application can use for drawing and for capturing events. By overriding the paint() method, the canvas can be used for anything from simple line drawings to full-scale custom components.

Since:

1.0

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
protected class	Canvas.AccessibleAWTCanvas This class provides accessibility support for the canvas.

Nested classes/interfaces inherited from class java.awt.Component

Component.AccessibleAWTComponent, Component.BltBufferStrategy, Component.FlipBufferStrategy

Field Summary

Fields inherited from class java.awt.Component

BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

Fields inherited from interface java.awt.image.ImageObserver

ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH

Constructor Summary

Constructors

Constructor and Description
Canvas() Initializes a new instance of Canvas.
Canvas(GraphicsConfiguration graphicsConfiguration) Initializes a new instance of Canvas with the supplied graphics configuration.

Method Summary

Methods

Modifier and Type	Method and Description
void	addNotify() Creates the native peer for this object.
void	createBufferStrategy(int numBuffers) Creates a buffering strategy that manages how this canvas is repainted.
void	createBufferStrategy(int numBuffers, BufferCapabilities caps) Creates a buffering strategy that manages how this canvas is repainted.
AccessibleContext	getAccessibleContext() Gets the AccessibleContext associated with this Canvas.
BufferStrategy	getBufferStrategy() Returns the buffer strategy used by the canvas.
void	paint(Graphics gfx) Repaints the canvas window.
void	update(Graphics graphics) Updates the canvas in response to a request to repaint() it.

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addHierarchyBoundsListener, addHierarchyListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addMouseWheelListener, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentListeners, getComponentOrientation, getCursor, getDropTarget, getFocusCycleRootAncestor, getFocusListeners, getFocusTraversalKeys, getFocusTraversalKeysEnabled, getFont, getFontMetrics, getForeground, getGraphics, getGraphicsConfiguration, getHeight, getHierarchyBoundsListeners, getHierarchyListeners, getIgnoreRepaint, getInputContext, getInputMethodListeners, getInputMethodRequests, getKeyListeners, getListeners, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getMinimumSize, getMouseListeners, getMouseMotionListeners, getMousePosition, getMouseWheelListeners, getName, getParent, getPeer, getPreferredSize, getPropertyChangeListeners, getPropertyChangeListeners, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isBackgroundSet, isCursorSet, isDisplayable, isDoubleBuffered, isEnabled, isFocusable, isFocusCycleRoot, isFocusOwner, isFocusTraversable, isFontSet, isForegroundSet, isLightweight, isMaximumSizeSet, isMinimumSizeSet, isOpaque, isPreferredSizeSet, isShowing, isValid, isVisible, keyDown, keyUp, layout, list, list, list, list, list, locate, location, lostFocus, minimumSize, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paintAll, paramString, postEvent, preferredSize, prepareImage, prepareImage, print, printAll, processComponentEvent, processEvent, processFocusEvent, processHierarchyBoundsEvent, processHierarchyEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, processMouseWheelEvent, remove, removeComponentListener, removeFocusListener, removeHierarchyBoundsListener, removeHierarchyListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removeMouseWheelListener, removeNotify, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, validate

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

Canvas

public Canvas()

Initializes a new instance of Canvas.

Canvas

public Canvas(GraphicsConfiguration graphicsConfiguration)

Initializes a new instance of Canvas with the supplied graphics configuration.

Parameters:

graphicsConfiguration - the graphics configuration to use for this particular canvas.

Method Detail

addNotify

public void addNotify()

Creates the native peer for this object.

Overrides:

addNotify in class Component

See Also:

Component.isDisplayable(), Component.removeNotify()

paint

public void paint(Graphics gfx)

Repaints the canvas window. This method should be overridden by a subclass to do something useful, as this method simply paints the window with the background color.

Overrides:

paint in class Component

Parameters:

gfx - the Graphics to use for painting

See Also:

Component.update(Graphics)

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this Canvas. The context is created, if necessary.

Specified by:

getAccessibleContext in interface Accessible

Overrides:

getAccessibleContext in class Component

Returns:

the associated context

createBufferStrategy

public void createBufferStrategy(int numBuffers)

Creates a buffering strategy that manages how this canvas is repainted. This method attempts to create the optimum strategy based on the desired number of buffers. Hardware or software acceleration may be used. createBufferStrategy attempts different levels of optimization, but guarantees that some strategy with the requested number of buffers will be created even if it is not optimal. First it attempts to create a page flipping strategy, then an accelerated blitting strategy, then an unaccelerated blitting strategy. Calling this method causes any existing buffer strategy to be destroyed.

Parameters:

numBuffers - the number of buffers in this strategy

Throws:

IllegalArgumentException - if requested number of buffers is less than one

IllegalStateException - if this canvas is not displayable

Since:

1.4

createBufferStrategy

public void createBufferStrategy(int numBuffers,
                        BufferCapabilities caps)
                          throws AWTException

Creates a buffering strategy that manages how this canvas is repainted. This method attempts to create a strategy based on the specified capabilities and throws an exception if the requested strategy is not supported. Calling this method causes any existing buffer strategy to be destroyed.

Parameters:

numBuffers - the number of buffers in this strategy

caps - the requested buffering capabilities

Throws:

AWTException - if the requested capabilities are not supported

IllegalArgumentException - if requested number of buffers is less than one or if caps is null

Since:

1.4

getBufferStrategy

public BufferStrategy getBufferStrategy()

Returns the buffer strategy used by the canvas.

Returns:

the buffer strategy.

Since:

1.4

update

public void update(Graphics graphics)

Updates the canvas in response to a request to repaint() it. The canvas is cleared with the current background colour, before paint() is called to add the new contents. Subclasses which override this method should either call this method via super.update(graphics) or re-implement this behaviour, so as to ensure that the canvas is clear before painting takes place.

Overrides:

update in class Component

Parameters:

graphics - the graphics context.

See Also:

Component.paint(Graphics), Component.repaint()