c# 異常處理try catch finally_throw

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

                    //throw引發異常，就會在程式碼塊中匹配查詢catch異常處理塊。就去執行相區配的catch異常處程式碼塊
                    throw new System.Exception();//throw異常物件,new ；throw主動引發異常

     
                }
                int n = (int)obj;
            }
            catch (System.Exception ex)
            {
                MessageBox.Show("捕獲異常" + ex.Message);
            }
            finally //finally必須執行,一般用於釋放佔用系統的資源
            {
                this.Close();//關閉窗體
            }