6.1.1 �N���XButton.java

package josx.platform.rcx;

/**
 * Abstraction for an RCX button.
 * Example:<p>
 * <code><pre>
 *    Button.RUN.waitForPressAndRelease();
 *    Sound.playTone (1000, 1);
 * </pre></code>
 */
public class Button
{
  /**
   * The Run button.
   */
  public static final Button RUN
                = new Button (0x01);
  /**
   * The View button.
   */
  public static final Button VIEW
                = new Button (0x02);
  /**
   * The Prgm button.
   */
  public static final Button PRGM
                = new Button (0x04);
  
  /**
   * Array containing VIEW,
   *  PRGM and RUN, in that order.
   */

  public static final Button[] BUTTONS
               = { Button.RUN,
                   Button.VIEW,
                   Button.PRGM };
  
  private int iCode;
  private ButtonListener[] iListeners
               = new ButtonListener[4];
  private int iNumListeners;
  
  private Button (int aCode)
  {
    iCode = aCode;
  }

  /**
   * Return the ID of the button.
   * One of 1, 2 or 4.
   */
  public final int getId()
  {
    return iCode;
  }
    
  /**
   * @return <code>true</code> if button
   * is pressed, <code>false</code> otherwise.
   */
  public final boolean isPressed()
  {
    return (readButtons() & iCode) != 0;
  }

  /**
   * Wait until the button is released.
   */
  public final void waitForPressAndRelease()
                throws InterruptedException
  {
    Poll poller = new Poll();
    do {
        poller.poll(iCode <<
                Poll.BUTTON_MASK_SHIFT, 0);
    } while (isPressed());
  }

  /**
   * Adds a listener of button events.
   * Each button can serve at most
   * 4 listeners.
   */
  public synchronized void
     addButtonListener (ButtonListener aListener)
  {
    if (iListeners == null)
    {
      iListeners = new ButtonListener[4];
    }
    iListeners[iNumListeners++] = aListener;
    ListenerThread.get().addButtonToMask(iCode);
  }

  /**
   * <i>Low-level API</i> that reads
   *   status of buttons.
   * @return An integer with possibly
   *   some bits set: 0x02 (view button pressed)
   * 0x04 (prgm button pressed),
   * 0x01 (run button pressed).
   *   If all buttons 
   * are released, this method returns 0.
   */
  public static int readButtons()
  {
    synchronized (Memory.MONITOR)
    {
      int pAddr = Memory.iAuxDataAddr;
      ROM.call ((short) 0x1fb6,
                (short) 0x3000,
                (short) pAddr);
      return Memory.readShort (pAddr);
    }
  }

  synchronized void callListeners()
  {
    for( int i = 0; i < iNumListeners; i++) {
      if( isPressed())
        iListeners[i].buttonPressed( this);
      else
        iListeners[i].buttonReleased( this);
    }
  }
}