//将字符串转换为数字

                   double d1 = Double.parseDouble(number1);

                   double d2 = Double.parseDouble(number2);

                   //判断运算符

                   if(opr.equals("+")){

                            return "" + (d1 + d2);

                   }

                   if(opr.equals("-")){

                            return "" + (d1 - d2);

                   }

                   if(opr.equals("*")){

                            return "" + (d1 * d2);

                   }

                   if(opr.equals("/")){

                            return "" + (d1 / d2);

                   }

                   return "0"; //运算符错误时返回0

         }

       

         /**

          *计算以后的处理

          * @param answer计算结果

          * @param index参与计算的三个字符串中第一个字符串的起始位置

          * @param v存储字符串的容器

          */

         private static void handle(String answer,int index,Vector v){

                   //删除计算过的字符串

                   for(int i = 0;i < 3;i++){

                            v.remove(index);

                   }

                   //将计算结果插入到index位置

                   v.insertElementAt(answer, index);

         }

}

        该程序的运行结果为：

                   13.0