C#3.0学习笔记(3)异常处理程序try catch语句

一，  什么叫异常？

       异常就是程序运行时的错误，它违反了一个系统约束或应用程序约束，或出    现了在正常操作时未预料的情形。如用0去除一个数时就会发生异常。

二，  try…catch…finally…语句的结构？

       未例：

       try

       {

              Statement;

       }

       catch(…)

       {

              Statement;

       }

       finally

       {

              Statement;

       }

1、 try块包括正被异常保护的代码。

2、 catch块是处理异常的代码块，也称异常处理程序。

3、 finally块是在所有情况下无论如何都要执行的代码，无论有没有异常发生。

三，  综合示例:

       namespace try_catch

{

    class Program

    {

        static voidMain(string[] args)

        {

            MyClass mc = new MyClass();

            try

            {

                mc.A();

            }

            catch (DivideByZeroException)

            {

                Console.WriteLine("catch clause inMain()");

            }

            finally

            {

                Console.WriteLine("finally clause inMain()");

            }

            Console.WriteLine("After try statement inMain.");

            Console.WriteLine("   --keep running!");

        }

    }

    class MyClass

    {

        public void A()

        {

            try

            {

                B();

            }

            catch (System.NullReferenceException)

            {

                Console.WriteLine("catch clause in A()");

            }

            finally

            {

                Console.WriteLine("finally clause in A()");

            }

        }

        protected void B()

        {

            int x = 10, y = 0;

            try

            {

                x /= y;

            }

            catch (System.IndexOutOfRangeException)

            {

                Console.WriteLine("catch clause in B()");

            }

            finally

            {

                Console.WriteLine("finally clause in B()");

            }

        }

    }

}

程序输出结果为：

finally clause in B()

finally clause in A()

catch clause inMain()

finally clause inMain()

After try statement inMain.

   --keep running.