canvas.java

有关j2me的很好的例子可以研究一下

     *
     * <P>Constant value 9 is set to GAME_A.</P>
     */
    public static final int GAME_A = 9; 
    
    /**
     * <P>Constant for the general purpose "B" game action.</P>
     *
     * <P>Constant value 10 is set to GAME_B.</P>
     */
    public static final int GAME_B = 10; 
    
    /**
     * <P>Constant for the general purpose "C" game action.</P>
     *
     * <P>Constant value 11 is set to GAME_C.</P>
     */
    public static final int GAME_C = 11;
    
    /**
     * <P>Constant for the general purpose "D" game action.</P>
     *
     * <P>Constant value 12 is set to GAME_D.</P>
     */
    public static final int GAME_D = 12; 
    
    /**
     * <P>keyCode for ITU-T key 0.</P>
     *
     * <P>Constant value 48 is set to KEY_NUM0.</P>
     */
    public static final int KEY_NUM0  =  48;
    
    /**
     * <P>keyCode for ITU-T key 1.</P>
     *
     * <P>Constant value 49 is set to KEY_NUM1.</P>
     */
    public static final int KEY_NUM1  =  49;
    
    /**
     * <P>keyCode for ITU-T key 2.</P>
     *
     * <P>Constant value 50 is set to KEY_NUM2.</P>
     */
    public static final int KEY_NUM2  =  50;
    
    /**
     * <P>keyCode for ITU-T key 3.</P>
     *
     * <P>Constant value 51 is set to KEY_NUM3.</P>
     */
    public static final int KEY_NUM3 = 51;
    
    /**
     * <P>keyCode for ITU-T key 4.</P>
     *
     * <P>Constant value 52 is set to KEY_NUM4.</P>
     */
    public static final int KEY_NUM4 = 52;
    
    /**
     * <P>keyCode for ITU-T key 5.</P>
     *
     * <P>Constant value 53 is set to KEY_NUM5.</P>
     */
    public static final int KEY_NUM5 = 53;
    
    /**
     * <P>keyCode for ITU-T key 6.</P>
     *
     * <P>Constant value 54 is set to KEY_NUM6.</P>
     */
    public static final int KEY_NUM6 = 54;
    
    /**
     * <P>keyCode for ITU-T key 7.</P>
     *
     * <P>Constant value 55 is set to KEY_NUM7.</P>
     */
    public static final int KEY_NUM7 = 55;
    
    /**
     * <P>keyCode for ITU-T key 8.</P>
     *
     * <P>Constant value 56 is set to KEY_NUM8.</P>
     */
    public static final int KEY_NUM8 = 56;
    
    /**
     * <P>keyCode for ITU-T key 9.</P>
     *
     * <P>Constant value 57 is set to KEY_NUM09.</P>
     */
    public static final int KEY_NUM9 = 57;
    
    /**
     * <P>keyCode for ITU-T key "star" (*).</P>
     *
     * <P>Constant value 42 is set to KEY_STAR.</P>
     */
    public static final int KEY_STAR = 42;
    
    /**
     * <P>keyCode for ITU-T key "pound" (#).</P>
     *
     * <P>Constant value 35 is set to KEY_POUND.</P>
     */
    public static final int KEY_POUND = 35;

    /**
     * Constructs a new Canvas object.
     */
    protected Canvas()  { }
    
    /**
     * Gets width of the displayable area in pixels. The value is unchanged
     * during the execution of the application and all Canvases will 
     * have the same value.
     * @return width of the displayable area
     */
    public int getWidth() {
        // SYNC NOTE: return of atomic value, no locking necessary
        return Display.WIDTH;
    }

    
    /**
     * Gets height of the displayable area in pixels. The value is unchanged
     * during the execution of the application and all Canvases will
     * have the same value.
     * @return height of the displayable area
     */
    public int getHeight() {
        // SYNC NOTE: return of atomic value, no locking necessary
        return Display.HEIGHT;
    }
    
    /**
     * Checks if the Graphics is double buffered by the implementation.
     * @return true if double buffered, false otherwise.
     */
    public boolean isDoubleBuffered() {
        // SYNC NOTE: return of atomic value, no locking necessary
        return Display.IS_DOUBLE_BUFFERED;
    }

    /**
     * Checks if the platform supports pointer press and release events.
     * @return true if the device supports pointer events
     */
    public boolean hasPointerEvents() {
        // SYNC NOTE: return of atomic value, no locking necessary
        return Display.POINTER_SUPPORTED;
    }
    
    /**
     * Checks if the platform supports pointer motion events (pointer dragged).
     * Applications may use this method to determine if the platform is capable
     * of supporting motion events.
     * @return true if the device supports pointer motion events
     */
    public boolean hasPointerMotionEvents() {
        // SYNC NOTE: return of atomic value, no locking necessary
        return Display.MOTION_SUPPORTED;
    }
    
    /**
     * Checks if the platform can generate repeat events when key
     * is kept down.
     * @return true if the device supports repeat events
     */
    public boolean hasRepeatEvents() { 
        // SYNC NOTE: return of atomic value, no locking necessary
        return Display.REPEAT_SUPPORTED;
    }
    
    /**
     * <p>Gets a key code that corresponds to the specified game action on the
     * device.  The implementation is required to provide a mapping for every
     * game action, so this method will always return a valid key code for
     * every game action.  See <a href="#gameactions">above</a> for further
     * discussion of game actions.</p>
     * 
     * <p>Note that a key code is associated with at most one game action,
     * whereas a game action may be associated with several key codes.  Then,
     * supposing that <code>g</code> is a valid game action and <code>k</code>
     * is a valid key code for a key associated with a game action, consider
     * the following expressions:</p>
     *
     * <pre>
     *    g == getGameAction(getKeyCode(g))     // (1)
     *    k == getKeyCode(getGameAction(k))     // (2)
     * </pre>
     *
     * <p>Expression (1) is <em>always</em> true.  However, expression (2) might
     * be true but is <em>not necessarily</em> true.</p>
     *
     * <P>The mapping between key codes and game actions
     * will not change during the execution of the application.</P>
     *
     * @param gameAction the game action
     * @return a key code corresponding to this game action
     * @throws IllegalArgumentException if gameAction is not a valid game action
     */
    public int getKeyCode(int gameAction) {
        // SYNC NOTE: no locking necessary as we are doing a static
        // table lookup and getKeyCode() is implemented natively
        int n = Display.getKeyCode(gameAction);

        if (n == 0) {
            throw new IllegalArgumentException();
        }

        return n;
    }
    
    /**
     * <p> Gets an informative key string for a key. The string returned will
     * resemble the text physically printed on the key.  This string is 
     * suitable for displaying to the user.  For example, on a device
     * with function keys F1 through F4, calling this method on the keyCode for
     * the F1 key will return the string "F1". A typical use for this string
     * will be to compose help text such as "Press F1 to proceed." </p>
     *
     * <p> This method will return a non-empty string for every valid key code.
     * </p>
     *
     * <p> There is no direct mapping from game actions to key names. To get
     * the string name for a game action GAME_A, the application must call </p>
     *
     * <pre>
     *    getKeyName(getKeyCode(GAME_A))
     * </pre>
     *
     * @param keyCode the key code being requested
     * @return a string name for the key
     * @throws IllegalArgumentException if keyCode is not a valid key code
     */
    public String getKeyName(int keyCode) {
        // SYNC NOTE: no locking necessary as we are doing a static
        // table lookup and getKeyName() is implemented natively
        String s = Display.getKeyName(keyCode);

        if (s == null) {
            throw new IllegalArgumentException();
        }

        return s;
    }

    /**
     * <p>Gets the game action associated with the given key code of the
     * device.  Returns zero if no game action is associated with this key
     * code.  See <a href="#gameactions">above</a> for further discussion of
     * game actions.  </p>
     *
     * <P>The mapping between key codes and game actions
     * will not change during the execution of the application.</P>
     * 
     * @param keyCode the key code
     * @return the game action corresponding to this key, or 0 if none
     * @throws IllegalArgumentException if keyCode is not a valid key code
     */