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java.lang.Object java.awt.Component java.awt.Canvas
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.
Nested Class Summary | |
protected class |
Canvas.AccessibleAWTCanvas
This class implements accessibility support for the Canvas class. |
Nested classes inherited from class java.awt.Component |
Component.AccessibleAWTComponent, Component.AWTTreeLock, Component.BltBufferStrategy, Component.FlipBufferStrategy |
Field Summary | |
private static String |
base
|
private static int |
nameCounter
|
private static long |
serialVersionUID
|
Fields inherited from interface java.awt.image.ImageObserver |
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH |
Constructor Summary | |
Canvas()
Constructs a new Canvas. |
|
Canvas(GraphicsConfiguration config)
Constructs a new Canvas given a GraphicsConfiguration object. |
Method Summary | |
void |
addNotify()
Creates the peer of the canvas. |
(package private) String |
constructComponentName()
Construct a name for this component. |
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. |
javax.accessibility.AccessibleContext |
getAccessibleContext()
Gets the AccessibleContext associated with this Canvas. |
BufferStrategy |
getBufferStrategy()
|
void |
paint(Graphics g)
Paints this canvas. |
(package private) boolean |
postsOldMouseEvents()
|
void |
update(Graphics g)
Updates this canvas. |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Field Detail |
private static final String base
private static int nameCounter
private static final long serialVersionUID
Constructor Detail |
public Canvas()
public Canvas(GraphicsConfiguration config)
config
- a reference to a GraphicsConfiguration object.GraphicsConfiguration
Method Detail |
String constructComponentName()
constructComponentName
in class Component
public void addNotify()
addNotify
in class Component
Toolkit.createCanvas(java.awt.Canvas)
,
Component.getToolkit()
public void paint(Graphics g)
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).
paint
in class Component
g
- the specified Graphics contextupdate(Graphics)
,
Component.paint(Graphics)
public void update(Graphics g)
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.
update
in class Component
g
- the specified Graphics contextpaint(Graphics)
,
Component.update(Graphics)
boolean postsOldMouseEvents()
postsOldMouseEvents
in class Component
public void createBufferStrategy(int numBuffers)
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.
createBufferStrategy
in class Component
numBuffers
- number of buffers to create, including the front buffer
IllegalArgumentException
- if numBuffers is less than 1.
IllegalStateException
- if the component is not displayableComponent.isDisplayable()
,
getBufferStrategy()
public void createBufferStrategy(int numBuffers, BufferCapabilities caps) throws AWTException
Each time this method is called, the existing buffer strategy for this component is discarded.
createBufferStrategy
in class Component
numBuffers
- number of buffers to createcaps
- the required capabilities for creating the buffer strategy;
cannot be null
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
getBufferStrategy()
public BufferStrategy getBufferStrategy()
getBufferStrategy
in class Component
createBufferStrategy(int)
public javax.accessibility.AccessibleContext getAccessibleContext()
getAccessibleContext
in interface javax.accessibility.Accessible
getAccessibleContext
in class Component
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