import java.awt.*;
import java.applet.*;
public class c3_6 extends Applet
{
    public void paint(Graphics g)
    {
   
    int k;
    int grade=86;
    k=grade/10;
    switch(k)
       {
        case 10:
        case 9:
        g.drawString("成绩:优",25,25); break;
        case 8:
        case 7:
        g.drawString("成绩:良",25,25); break;
        case 6:
        g.drawString("成绩:及格",25,25); break;
        default: g.drawString("成绩:不及格。",25,25);
       }
     }
}

java一个程序编译通过，但就是执行出错，出现 Exception in thread "main" java.lang.NoSuchMethodError:main 这样的错误！