Java java.awt Class Canvas（JDK8）

Constructor Detail

• Canvas

  public Canvas()

  Constructs a new Canvas.

• Canvas

  public Canvas(GraphicsConfiguration config)

  Constructs a new Canvas given a GraphicsConfiguration object.

  Parameters:

  config - a reference to a GraphicsConfiguration object.

  See Also:

  GraphicsConfiguration

Method Detail

• 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:

  Toolkit.createCanvas(java.awt.Canvas), 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