try
            {
                object bj = null;
                if (obj is Nullable)
                {

                    //throw引发异常，就会在代码块中匹配查找catch异常处理块。就去执行相区配的catch异常处代码块
                    throw new System.Exception();//throw异常对象,new ；throw主动引发异常

     
                }
                int n = (int)obj;
            }
            catch (System.Exception ex)
            {
                MessageBox.Show("捕获异常" + ex.Message);
            }
            finally //finally必须执行,一般用于释放占用系统的资源
            {
                this.Close();//关闭窗体
            }