public class rectangle
      {
           double chang;
            double kuan;
   
               void rectangle()
     {
                     mianji=chang*kuan;
                       System.out.ptintln(mianji);
     }
                  void rectangl(){
                      {
                       zhouchang=(chang=kuan)*2;
                         System.out.ptintln(zhouchang);
     }
                  }
public static void main(String[] args)
    {
    rectangle r=new rectangle();
    r.chang=3;
    r.kuan=4;
    r.zhouchang;
    r.mianji;
   
}
}

呵呵，我Java好菜的，谢谢关照了。。