java.awt

Class Canvas

Implemented Interfaces:
Accessible, ImageObserver, MenuContainer, Serializable

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

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

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

Method Summary

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, addNotify, addPropertyChangeListener, addPropertyChangeListener, applyComponentOrientation, areFocusTraversalKeysSet, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, createVolatileImage, createVolatileImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, extends EventListener> T[] getListeners, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, firePropertyChange, getAccessibleContext, 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, 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, isFocusCycleRoot, isFocusOwner, isFocusTraversable, isFocusable, 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, paint, 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, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFocusable, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, update, validate

Methods inherited from class java.lang.Object

clone, equals, extends Object> getClass, finalize, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Details

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 Details

addNotify

public void addNotify()
Creates the native peer for this object.
Overrides:
addNotify in interface Component

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

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 interface Component
Returns:
the associated context

getBufferStrategy

public BufferStrategy getBufferStrategy()
Returns the buffer strategy used by the canvas.
Returns:
the buffer strategy.
Since:
1.4

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 interface Component
Parameters:
gfx - the Graphics to use for painting

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 interface Component
Parameters:
graphics - the graphics context.

Canvas.java -- Copyright (C) 1999, 2000, 2002, 2004 Free Software Foundation This file is part of GNU Classpath. GNU Classpath is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2, or (at your option) any later version. GNU Classpath is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with GNU Classpath; see the file COPYING. If not, write to the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA. Linking this library statically or dynamically with other modules is making a combined work based on this library. Thus, the terms and conditions of the GNU General Public License cover the whole combination. As a special exception, the copyright holders of this library give you permission to link this library with independent modules to produce an executable, regardless of the license terms of these independent modules, and to copy and distribute the resulting executable under terms of your choice, provided that you also meet, for each linked independent module, the terms and conditions of the license of that module. An independent module is a module which is not derived from or based on this library. If you modify this library, you may extend this exception to your version of the library, but you are not obligated to do so. If you do not wish to do so, delete this exception statement from your version.