stopwatch.java

j2me的1套UI框架,可以帮助开发者迅速的开发j2me应用程序.

package org.j4me.examples.ui;

import java.util.*;
import javax.microedition.lcdui.*;
import org.j4me.ui.*;
import org.j4me.ui.components.*;

/**
 * The stopwatch can be started and stopped to time an event.
 * When restarted the watch resets back to zero seconds before
 * timing.
 * <p>
 * Demonstrates how to use an empty canvas.  It also demonstrates
 * manually laying out a component (specifically a <code>Label</code>)
 * on a canvas.
 */
public class Stopwatch
	extends DeviceScreen
{
	/**
	 * The screen to return to once this one is canceled.
	 */
	private final DeviceScreen previous;
	
	/**
	 * The system time that the stopwatch started.  If the stopwatch
	 * isn't running, this will be -1.
	 */
	private long startTime = -1;
	
	/**
	 * A label showing how much time has elapsed.  This is painted onto
	 * the center of the canvas while the stopwatch is running.
	 */
	private Label elapsedTime;
	
	/**
	 * A timer to handle stopwatch timing.
	 */
	private Timer timer;
	
	/**
	 * Initializes the screen.
	 * 
	 * @param previous is the screen that this one will return to when
	 *  the user backs out of it.
	 */
	public Stopwatch (DeviceScreen previous)
	{
		this.previous = previous;
		
		setTitle( "Stopwatch" );
		setMenuText( "Back", "Start" );
		
		// Create the label that shows the time.
		elapsedTime = new Label();
		elapsedTime.setLabel( "Press Start to begin" );
		elapsedTime.setHorizontalAlignment( Graphics.HCENTER );
		Font font = Font.getFont( Font.FACE_MONOSPACE, Font.STYLE_BOLD, Font.SIZE_LARGE );
		elapsedTime.setFont( font );
	}

	/**
	 * Called when the user presses the left side button which takes us
	 * back to the previous screen.
	 */
	protected void declineNotify ()
	{
		if ( previous != null )
		{
			previous.show();
		}
	}

	/**
	 * Called when the user presses the right side button which starts
	 * or stops the stopwatch.
	 */
	protected void acceptNotify ()
	{
		if ( startTime < 0 )
		{
			setMenuText( getLeftMenuText(), "Stop" );
			
			// Start the clock.
			startTime = System.currentTimeMillis();
			
			if ( timer != null )
			{
				timer.cancel();
			}
			
			timer = new Timer();
			timer.schedule( new StopwatchTimerTask(), 0, 15 );  // Every 15 milliseconds
		}
		else
		{
			setMenuText( getLeftMenuText(), "Start" );
			
			// Stop the clock.
			startTime = -1;
			
			if ( timer != null )
			{
				timer.cancel();
				timer = null;
			}
		}
		
		repaint();
	}

	/**
	 * Called when any key is pressed.
	 * 
	 * @see org.j4me.ui.DeviceScreen#keyPressed(int)
	 */
	protected void keyPressed (int keyCode)
	{
		// Let the fire key start/stop the timer.
		if ( keyCode == FIRE )
		{
			acceptNotify();
		}
			
		// Forward the event for further processing.
		super.keyPressed( keyCode );
	}

	/**
	 * Implements stopwatch functionality.
	 */
	private final class StopwatchTimerTask
		extends TimerTask
	{
		public void run ()
		{
			synchronized ( Stopwatch.this )
			{
				long duration = System.currentTimeMillis() - startTime;
				long milliseconds = duration % 1000;
				long seconds = duration / 1000;
				long minutes = seconds / 60;
				seconds %= 60;
	
				StringBuffer buffer = new StringBuffer();
				buffer.append( minutes );
				buffer.append( ":" );
				
				if ( seconds < 10 ) buffer.append( "0" );
				buffer.append( seconds );
				buffer.append( "." );
				
				if ( milliseconds < 10 ) buffer.append( "00" );
				else if ( milliseconds < 100 ) buffer.append( "0" );
				buffer.append( milliseconds );
				
				String time = buffer.toString();
				elapsedTime.setLabel( time );
				
				repaint();
			}
		}
	}

	/**
	 * When the canvas becomes visible notify the component it is
	 * going to be displayed.  This lets it initialize any resources
	 * it requires.
	 * 
	 * @see DeviceScreen#showNotify()
	 */
	public void showNotify ()
	{
		// Inform the components they are visible.
		elapsedTime.show( true );
	}

	/**
	 * When the canvas is removed notify the component it is
	 * no longer displayed.  This lets it clean up any resources it
	 * used.
	 * 
	 * @see DeviceScreen#hideNotify()
	 */
	public void hideNotify ()
	{
		// Inform the components they are no longer visible.
		elapsedTime.show( false );
		
		// Stop the timer.
		if ( timer != null )
		{
			timer.cancel();
			timer = null;
		}
	}

	/**
	 * Paints the blank area of the canvas.  This just shows how long
	 * the timer has been running.
	 */
	protected synchronized void paint (Graphics g)
	{
		int width = getWidth();
		int height = getHeight();
		
		// Get the height of the elapsed time label.
		Theme theme = UIManager.getTheme();
		int[] dimensions = elapsedTime.getPreferredSize( theme, width, height );
		int labelHeight = dimensions[1];
		
		// Vertically center the label.
		int labelY = (height - labelHeight) / 2;
			
		// Paint the label.
		elapsedTime.paint( g, theme, this, 0, labelY, width, height, true );
	}
}