Why is try {...} finally {...} good; try {...} catch{} bad?
I have seen people say that it is bad form to use catch with no arguments, especially if that catch doesn't do anything:
StreamReader reader=new StreamReader("myfile.txt");
try
{
int i = 5 / 0;
}
catch // No args, so it will catch any exception
{}
reader.Close();
However, this is considered good form:
StreamReader reader=new StreamReader("myfile.txt");
try
{
int i = 5 / 0;
}
finally // Will execute despite any exception
{
reader.Close();
}
As far as I can tell, the only difference between putting cleanup code in a finally block and putting cleanup code after the try..catch blocks is if you have return statements in your try block (in that case, the cleanup code in finally will run, but code after the try..catch will not).
Otherwise, what's so special about finally?
The big difference is that try...catch will swallow the exception, hiding the fact that an error occurred. try..finally will run your cleanup code and then the exception will keep going, to be handled by something that knows what to do with it.
"Finally" is a statement of "Something you must always do to make sure program state is sane". As such, it's always good form to have one, if there's any possibility that exceptions may throw off the program state. The compiler also goes to great lengths to ensure that your Finally code is run.
"Catch" is a statement of "I can recover from this exception". You should only recover from exceptions you really can correct - catch without arguments says "Hey, I can recover from anything!", which is nearly always untrue.
If it were possible to recover from every exception, then it would really be a semantic quibble, about what you're declaring your intent to be. However, it's not, and almost certainly frames above yours will be better equipped to handle certain exceptions. As such, use finally, get your cleanup code run for free, but still let more knowledgeable handlers deal with the issue.
Because when that one single line throws an exception, you wouldn't know it.
With the first block of code, the exception will simply be absorbed , the program will continue to execute even when the state of the program might be wrong.
With the second block, the exception will be thrown and bubbles up but the reader.Close() is still guaranteed to run.
If an exception is not expected, then don't put a try..catch block just so, it'll be hard to debug later when the program went into a bad state and you don't have an idea why.
链接地址: http://www.djcxy.com/p/12802.html上一篇: “终于”总是用Python执行吗？