编了一段程序如下，请问要如何命名，还有为什么，急求在线等；
import java.applet.Applet;
import java.awt.*;
public class helloworld extends Applet
{
boolean mousedownbool=false;
int mousex,mousey;
public void paint(Graphics g)
{
if(mousedownbool)
{
g.drawString("Hello world!",mousex,mousey);
}
}
public boolean mouseDown(Event evt,int x,int y)
{
mousex=x;
mousey=y;
mousedownbool=true;
repaint();
return true;
}
}