Module java.desktop
Package java.awt

Class 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

    • 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:
        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