Canvas (Java Platform SE 8 )
Keywords: java.awt.Canvas class
Date: 2016-07-28

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:
    JDK1.0
  See Also:
    Serialized Form

- - ### Nested Class Summary

    Nested Classes
    Modifier and Type | Class and Description
    --- | ---
    `protected class` | `Canvas.AccessibleAWTCanvas` This class implements accessibility support for the `Canvas` class.

    - ### Nested classes/interfaces inherited from class java.awt.Component

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

  - ### Field Summary

    - ### Fields inherited from class java.awt.Component

      `accessibleContext, 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

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

  - ### Method Summary

    All Methods Instance Methods Concrete Methods
    Modifier and Type | Method and 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 inherited from 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, getPeer, 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, requestFocusInWindow, requestFocusInWindow, reshape, resize, resize, revalidate, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFocusable, setFocusTraversalKeys, setFocusTraversalKeysEnabled, setFont, setForeground, setIgnoreRepaint, setLocale, setLocation, setLocation, setMaximumSize, setMinimumSize, setName, setPreferredSize, setSize, setSize, setVisible, show, show, size, toString, transferFocus, transferFocusBackward, transferFocusUpCycle, validate`

    - ### Methods inherited from class java.lang.Object

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

- - ### 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

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