为什么try{…}最后{…}好;尝试{…} catch{}坏?

我见过有人说，使用不带参数的catch是一种糟糕的形式，尤其是当catch什么都不做的时候:

StreamReader reader=new  StreamReader("myfile.txt");
try
{
  int i = 5 / 0;
}
catch   // No args, so it will catch any exception
{}
reader.Close();

然而，这被认为是良好的形式:

StreamReader reader=new  StreamReader("myfile.txt");
try
{
  int i = 5 / 0;
}
finally   // Will execute despite any exception
{
  reader.Close();
}

据我所知，将清理代码放在finally块和将清理代码放在try. catch块之后的唯一区别是，如果你在try块中有返回语句(在这种情况下，finally中的清理代码将运行，但try. catch块之后的代码将不会运行)。

否则，最后有什么特别的?

当前回答

摄自:这里

引发和捕获异常不应该作为方法成功执行的一部分常规发生。在开发类库时，必须让客户端代码有机会在执行可能引发异常的操作之前测试错误条件。例如，System.IO.FileStream提供了一个CanRead属性，可以在调用Read方法之前进行检查，以防止引发潜在的异常，如下所示的代码片段:

Dim str As Stream = GetStream() If (str.CanRead) Then '代码来读取流如果

The decision of whether to check the state of an object prior to invoking a particular method that may raise an exception depends on the expected state of the object. If a FileStream object is created using a file path that should exist and a constructor that should return a file in read mode, checking the CanRead property is not necessary; the inability to read the FileStream would be a violation of the expected behavior of the method calls made, and an exception should be raised. In contrast, if a method is documented as returning a FileStream reference that may or may not be readable, checking the CanRead property before attempting to read data is advisable.

To illustrate the performance impact that using a "run until exception" coding technique can cause, the performance of a cast, which throws an InvalidCastException if the cast fails, is compared to the C# as operator, which returns nulls if a cast fails. The performance of the two techniques is identical for the case where the cast is valid (see Test 8.05), but for the case where the cast is invalid, and using a cast causes an exception, using a cast is 600 times slower than using the as operator (see Test 8.06). The high-performance impact of the exception-throwing technique includes the cost of allocating, throwing, and catching the exception and the cost of subsequent garbage collection of the exception object, which means the instantaneous impact of throwing an exception is not this high. As more exceptions are thrown, frequent garbage collection becomes an issue, so the overall impact of the frequent use of an exception- throwing coding technique will be similar to Test 8.05.

2008-09-24 18:14:42

其他回答

Finally是可选的——如果没有资源可以清理，就没有理由使用“Finally”块。

2008-09-24 18:14:39

使用finally，您可以清理资源，即使您的catch语句将异常抛出给调用程序。与包含空catch语句的示例相比，差别不大。但是，如果在catch中执行了一些处理并抛出错误，或者甚至根本没有catch, finally仍然会运行。

2008-09-24 18:14:18

如果您不知道要捕获什么异常类型或如何处理它，那么使用catch语句是没有意义的。你应该把它留给上级，他们可能对情况有更多的了解，知道该怎么做。

在那里仍然应该有一个finally语句，以防出现异常，这样就可以在异常抛出给调用者之前清理资源。

2008-09-24 18:13:20

使用Try…Catch . .最后，如果您的方法知道如何在本地处理异常。异常发生在Try中，在Catch中处理，然后在Finally中完成清理。

如果你的方法不知道如何处理异常，但需要在异常发生后进行清理，请使用Try..最后

通过这种方式，异常被传播到调用方法，如果调用方法中有任何合适的Catch语句，则进行处理。如果当前方法或任何调用方法中没有异常处理程序，则应用程序将崩溃。