Module java.desktop

Package 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 Accessible

A Canvas component represents a blank rectangular area of the screen onto which the application can draw or from which the application can trap input events from the user.

An application must subclass the Canvas class in order to get useful functionality such as creating a custom component. The paint method must be overridden in order to perform custom graphics on the canvas.

Since:

1.0

See Also:

• Serialized Form

Nested Class Summary

Nested Classes

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

Nested classes/interfaces declared in class java.awt.Component

Component.AccessibleAWTComponent, Component.BaselineResizeBehavior, Component.BltBufferStrategy, Component.FlipBufferStrategy

Field Summary

Fields declared in class java.awt.Component

accessibleContext, BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT

Fields declared in interface java.awt.image.ImageObserver

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

Constructor Summary

Constructors

Constructor	Description
Canvas()	Constructs a new Canvas.
Canvas(GraphicsConfiguration config)	Constructs a new Canvas given a GraphicsConfiguration object.

Method Summary

Modifier and Type	Method	Description
void	addNotify()	Creates the peer of the canvas.
void	createBufferStrategy(int numBuffers)	Creates a new strategy for multi-buffering on this component.
void	createBufferStrategy(int numBuffers, BufferCapabilities caps)	Creates a new strategy for multi-buffering on this component with the required buffer capabilities.
AccessibleContext	getAccessibleContext()	Gets the AccessibleContext associated with this Canvas.
BufferStrategy	getBufferStrategy()	Returns the BufferStrategy used by this component.
void	paint(Graphics g)	Paints this canvas.
void	update(Graphics g)	Updates this canvas.

Methods declared in 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, getBaseline, getBaselineResizeBehavior, 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, 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, requestFocus, requestFocus, requestFocusInWindow, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setMixingCutoutShape, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, validate

Methods declared in class java.lang.Object

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

Constructor Details

Canvas

public Canvas()

Constructs a new Canvas.

Canvas

public Canvas(GraphicsConfiguration config)

Constructs a new Canvas given a GraphicsConfiguration object. If null is passed, then the default GraphicsConfiguration will be used.

Parameters:

config - a reference to a GraphicsConfiguration object or null

See Also:

• GraphicsConfiguration
• Component.getGraphicsConfiguration()

Method Details

addNotify

public void addNotify()

Creates the peer of the canvas. This peer allows you to change the user interface of the canvas without changing its functionality.

Overrides:

addNotify in class Component

See Also:

• Component.getToolkit()

paint

public void paint(Graphics g)

Paints this canvas.

Most applications that subclass Canvas should override this method in order to perform some useful operation (typically, custom painting of the canvas). The default operation is simply to clear the canvas. Applications that override this method need not call super.paint(g).

Overrides:

paint in class Component

Parameters:

g - the specified Graphics context

See Also:

• update(Graphics)
• Component.paint(Graphics)

update

public void update(Graphics g)

Updates this canvas.

This method is called in response to a call to repaint. The canvas is first cleared by filling it with the background color, and then completely redrawn by calling this canvas's paint method. Note: applications that override this method should either call super.update(g) or incorporate the functionality described above into their own code.

Overrides:

update in class Component

Parameters:

g - the specified Graphics context

See Also:

• paint(Graphics)
• Component.update(Graphics)

createBufferStrategy

public void createBufferStrategy(int numBuffers)

Creates a new strategy for multi-buffering on this component. Multi-buffering is useful for rendering performance. This method attempts to create the best strategy available with the number of buffers supplied. It will always create a BufferStrategy with that number of buffers. A page-flipping strategy is attempted first, then a blitting strategy using accelerated buffers. Finally, an unaccelerated blitting strategy is used.

Each time this method is called, the existing buffer strategy for this component is discarded.

Parameters:

numBuffers - number of buffers to create, including the front buffer

Throws:

IllegalArgumentException - if numBuffers is less than 1.

IllegalStateException - if the component is not displayable

Since:

1.4

See Also:

• Component.isDisplayable()
• getBufferStrategy()

createBufferStrategy

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

Creates a new strategy for multi-buffering on this component with the required buffer capabilities. This is useful, for example, if only accelerated memory or page flipping is desired (as specified by the buffer capabilities).

Each time this method is called, the existing buffer strategy for this component is discarded.

Parameters:

numBuffers - number of buffers to create

caps - the required capabilities for creating the buffer strategy; cannot be null

Throws:

AWTException - if the capabilities supplied could not be supported or met; this may happen, for example, if there is not enough accelerated memory currently available, or if page flipping is specified but not possible.

IllegalArgumentException - if numBuffers is less than 1, or if caps is null

Since:

1.4

See Also:

• getBufferStrategy()

getBufferStrategy

public BufferStrategy getBufferStrategy()

Returns the BufferStrategy used by this component. This method will return null if a BufferStrategy has not yet been created or has been disposed.

Returns:

the buffer strategy used by this component

Since:

1.4

See Also:

• createBufferStrategy(int)

getAccessibleContext

public AccessibleContext getAccessibleContext()

Gets the AccessibleContext associated with this Canvas. For canvases, the AccessibleContext takes the form of an AccessibleAWTCanvas. A new AccessibleAWTCanvas instance is created if necessary.

Specified by:

getAccessibleContext in interface Accessible

Overrides:

getAccessibleContext in class Component

Returns:

an AccessibleAWTCanvas that serves as the AccessibleContext of this Canvas

Since:

1.3