import java.applet.*;
import java.awt.*;

public class WalkingText extends Applet implements Runnable {
   protected String mesg = null;
   protected int  xloc, yloc, width, height, textWidth, textHeight;
   protected Thread t;
   protected boolean done = false;
   /** How long to nap for each move */
   protected int napTime = 150;

   /** Applet Initializer */
   public void init() {
      xloc = 0;

      //获得屏幕的大小
      width = getSize().width;
      height = getSize().height;

      if ((mesg = getParameter("text")) == null)
         mesg = "Hello World of Java";

      String pSize = getParameter("fontsize");
      if (pSize == null)
         pSize = "12";

      String fontName = getParameter("fontName");
      if (fontName == null)
         fontName = "Helvetica";

      // System.out.println("Font is " + pSize + " point " + fontName);
      Font f = new Font(fontName, Font.PLAIN, Integer.parseInt(pSize));
      setFont(f);

      FontMetrics fm = getToolkit().getFontMetrics(f);
      textWidth = fm.stringWidth(mesg);
      textHeight = fm.getHeight();


      // use textHeight in y coordinate calculation
      yloc = height - ((height-textHeight) / 2);
   }

   /** This is important: we create a thread, so we must kill it */
   public void stop() {
      done = true;
      t = null;
   }

   /** create the thread and start it. */
   public void start() {
      if (t == null)
         t = new Thread(this);
      done = false;
      t.start();
   }

   // Usage:
   public String[][] getParameterInfo() {
      String[][] params = {
         { "text", "text", "Text to walk across the screen" },
         { "fontName", "text", "Name of font to display in" },
         { "fontsize", "int", "How big to make the text" },
      };

      return params;
   }


   /** Run is called by the Thread class when there is work to do */
   public void run() {
      while (!done) {
         if ((xloc+=5) > getSize().width)
            xloc = 0;
         repaint();
         try {
            Thread.sleep(napTime);
         } catch (Exception e) {
            System.out.println("Who dares to interrupt my Sleep()? " + e);
         };
      }
   }

   /** Paint is called by Applet to redraw the screen */
   public void paint(Graphics g) {
      g.drawString(mesg, xloc, yloc);
   }
}