j-j2me-8-3.shtml

这是一本介绍J2ME 编程的书籍,里面有具体的实现过程讲解,是很好的入门书籍

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              应用程序 HelloWorld</font></b></td><td width="200" align="right"><nobr><font size="1" face="Verdana, Arial, Helvetica">第 3 页（共 6 页）</font></nobr></td></tr></table><br x="7"><br x="7"></p><font size="2" face="Verdana, Arial, Helvetica"><p>这个应用程序将在屏幕中央显示 "Hello World!" 和一个 Exit 按钮，按下后即终止该应用程序。HelloWorld.java 开始时使用下面的几行代码导入将在后面的 <code style="font-family: Courier New, Courier, monospace; font-size: 12">HelloWorld</code> 类中使用的类:
</p><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
    import com.sun.kjava.Button;
    import com.sun.kjava.Graphics;
    import com.sun.kjava.Spotlet;
</code></pre><p>
下面的代码行将 <code style="font-family: Courier New, Courier, monospace; font-size: 12">HelloWorld</code> 类定义为扩展 <code style="font-family: Courier New, Courier, monospace; font-size: 12">Spotlet</code>：
</p><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
    public class HelloWorld extends Spotlet
</code></pre><p>
请记住 <code style="font-family: Courier New, Courier, monospace; font-size: 12">Spotlet</code> 类提供用于处理事件的回调功能。在这个简单的示例中，我们只对一个事件感兴趣，即用户何时按下 Exit 按钮。下一个代码行存储对 Exit  
按钮的引用：
</p><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
    private static Button exitButton;
</code></pre><p>
如同在 J2SE 中一样，<code style="font-family: Courier New, Courier, monospace; font-size: 12">main()</code> 方法定义程序的主要入口点。对于 J2ME 应用程序，<code style="font-family: Courier New, Courier, monospace; font-size: 12">main</code> 也定义了入口点。在本例中，<code style="font-family: Courier New, Courier, monospace; font-size: 12">main()</code> 创建了一个新的 <code style="font-family: Courier New, Courier, monospace; font-size: 12">HelloWorld</code> 类的实例，它运行我们的应用程序。
</p><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
    public static void main(String[] args)
    {
       (new HelloWorld()).register(NO_EVENT_OPTIONS);
    }
</code></pre><p>
下一个代码块定义了构造程序。在构造程序中，我们首先创建一个 <code style="font-family: Courier New, Courier, monospace; font-size: 12">Button</code> 并为其加上 "Exit" 标签。按钮起初是不可见的。当我们得到对图形对象的引用后，此按钮成了一个可画的屏幕，先清屏然后在屏幕中央画出文本 "Hello World!"。最后，我们在屏幕上添加 Exit 按钮。
</p><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
      public HelloWorld()
      {
         // Create (initially invisible) the "Exit" button
         exitButton = new Button("Exit",70,145);

         // Get a reference to the graphics object;
         // i.e. the drawable screen
         Graphics g = Graphics.getGraphics();
         g.clearScreen();

         // Draw the text, "Hello World!" somewhere near the center
         g.drawString("Hello World!", 55, 45, g.PLAIN);

         // Draw the "Exit" button
         exitButton.paint();
      }
</code></pre><p>
最后，我们定义 <code style="font-family: Courier New, Courier, monospace; font-size: 12">penDown</code> 事件处理程序，用来简单地检查 Exit 按钮是否被按下。如果已按下，就退出应用程序。
</p><pre><code style="font-family: Courier New, Courier, monospace; font-size: 12">
      public void penDown(int x, int y)
      {
         // If the "Exit" button was pressed, end this application
         if (exitButton.pressed(x,y))
           System.exit(0);
      }
</code></pre><br x="7"></font></td></tr></table><TABLE border="0" cellpadding="0" cellspacing="0" width="100%"><TR><TD background="../i/sw-gold.gif"><a border="0" href="index.shtml" onMouseOver="iOver('topmain'); iOver('bottommain'); self.status=mainblurb; return true;" onMouseOut="iOut('topmain'); iOut('bottommain'); self.status=''; return true;"><img alt="主菜单" border="0" src="../i/main.gif" name="bottommain" width="77" height="15"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topsection'); iOver('bottomsection'); self.status=sectionblurb; return true;" onMouseOut="iOut('topsection'); iOut('bottomsection'); self.status=''; return true;" href="index8.shtml"><img alt="章节菜单" border="0" src="../i/section.gif" name="bottomsection" width="98" height="15"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topfeedback'); iOver('bottomfeedback'); self.status=feedbackblurb; return true;" onMouseOut="iOut('topfeedback'); iOut('bottomfeedback'); self.status=''; return true;" href="j-j2me-12-3.shtml"><img alt="给出此教程的反馈意见" border="0" src="../i/feedback.gif" name="bottomfeedback" width="80" height="15"></a></TD><TD width="100%" background="../i/sw-gold.gif"><img src="../i/c.gif" width="1" height="1"></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topprevious'); iOver('bottomprevious'); self.status=previousblurb; return true;" onMouseOut="iOut('topprevious'); iOut('bottomprevious'); self.status=''; return true;" href="j-j2me-8-2.shtml"><img alt="上一屏" border="0" src="../i/previous.gif" name="bottomprevious" width="77" height="15"></a></TD><TD background="../i/sw-gold.gif"><a border="0" onMouseOver="iOver('topnext'); iOver('bottomnext'); self.status=nextblurb; return true;" onMouseOut="iOut('topnext'); iOut('bottomnext'); self.status=''; return true;" href="j-j2me-8-4.shtml"><img alt="下一屏" border="0" src="../i/next.gif" name="bottomnext" width="60" height="15"></a></TD></TR><TR><TD width="150" height="1" bgcolor="#000000" colspan="6"><IMG alt="" height="1" width="150" src="../i/c.gif"></TD></TR></TABLE><!--#include virtual="/developerWorks/inc/tuto-inc/tuto-footer.inc" --></body></html>