You can use this identifier to get information about the exception that was thrown. This identifier is only available in the catch -block's scope. If you don't need the exception value, it could be omitted. The finally -block contains statements to execute after the try -block and catch -block s execute, but before the statements following the try Note that the finally -block executes regardless of whether an exception is thrown.
Also, if an exception is thrown, the statements in the finally -block execute even if no catch -block handles the exception. The following example shows one use case for the finally -block. The code opens a file and then executes statements that use the file; the finally -block makes sure the file always closes after it is used even if an exception was thrown.
Now, if we already caught the exception in the inner try -block by adding a catch -block. Any given exception will be caught only once by the nearest enclosing catch -block unless it is rethrown. Of course, any new exceptions raised in the "inner" block because the code in catch -block may do something that throws , will be caught by the "outer" block. If the finally -block returns a value, this value becomes the return value of the entire try-catch-finally statement, regardless of any return statements in the try and catch -blocks.
This includes exceptions thrown inside of the catch -block:. Add a comment. Active Oldest Votes. Obviously this is one of those questions where the only real answer is "it depends. Improve this answer. Matthew Flaschen k 47 47 gold badges silver badges bronze badges. John John Catching all exceptions at language borders to translate them is also good practice.
My basic rule of thumb is to catch all the exceptions you expect and anything else is a bug. JamesSugrue JamesSugrue Cheekysoft Cheekysoft The catch could be used to add additional information and then rethrow, right? Erik van Brakel Erik van Brakel Tundey Tundey 2, 1 1 gold badge 21 21 silver badges 26 26 bronze badges. Letting an exception bubble up does not mean showing it to the end user. You can and should show a generic error page, log it for investigation, and then fix the problem that caused the exception in the first place.
Does not answer question asked. Philippe Philippe 3, 3 3 gold badges 36 36 silver badges 55 55 bronze badges. The point is twofold I think. It is bad to code logic by exceptions, if you expect that file provided by user could not exist, there is a method to check that: File. KrzysztofCichocki - I know this is old, but actually, coding file logic using exceptions in this way is more correct. There's a great explanation by Eric Lippert here.
He terms this type "exogenous" exceptions. There is always a race-condition, where it can be deleted before you access it. What would happen if the code which called CriticalException also called Thread.
Abort Thread. Because the thread being aborted would be in a known state calling Abort , the normal hazards of that method wouldn't apply; code which does a catch Exception ex would catch the resulting thread-abort exception, but wouldn't stop it from propagating up the call chain. It would be better, of course, if there were some way a more meaningfully-named exception could behave likewise, but I know of no such feature in.
These cases are: The top of all threads By default, exceptions will vanish without a trace! Inside a main processing loop that you expect to never exit Inside a Loop processing a list of objects where one failure shouldn't stop others Top of the "main" thread--You might control a crash here, like dump a little data to stdout when you run out of memory.
If you have a "Runner" that runs code for instance, if someone adds a listener to you and you call the listener then when you run the code you should catch Exception to log the problem and let you continue notifying other listeners. Bill K Bill K Unpopular opinion: Not really.
Catch all of the errors you can meaningfully recover from. Sometimes that's all of them. Beefster Beefster 5 5 silver badges 19 19 bronze badges.
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Does ES6 make JavaScript frameworks obsolete? Podcast Do polyglots have an edge when it comes to mastering programming Featured on Meta. For example, on. For App Domain A to properly catch and handle the exception, it must be able to find the assembly that contains the exception thrown by App Domain B.
If App Domain B throws an exception that is contained in an assembly under its application base, but not under App Domain A's application base, App Domain A will not be able to find the exception, and the common language runtime will throw a FileNotFoundException exception. To avoid this situation, you can deploy the assembly that contains the exception information in two ways:. If the domains do not share a common application base, sign the assembly that contains the exception information with a strong name and deploy the assembly into the global assembly cache.
Write clear sentences and include ending punctuation. Each sentence in the string assigned to the Exception. Message property should end in a period. For example, "The log table has overflowed. The error message that the user sees is derived from the Exception. Message property of the exception that was thrown, and not from the name of the exception class. Typically, you assign a value to the Exception. Message property by passing the message string to the message argument of an Exception constructor.
For localized applications, you should provide a localized message string for every exception that your application can throw. You use resource files to provide localized error messages.
For information on localizing applications and retrieving localized strings, see the following articles:. Provide additional properties for an exception in addition to the custom message string only when there's a programmatic scenario where the additional information is useful.
The stack trace begins at the statement where the exception is thrown and ends at the catch statement that catches the exception.
It is common for a class to throw the same exception from different places in its implementation. To avoid excessive code, use helper methods that create the exception and return it.
In some cases, it's more appropriate to use the exception's constructor to build the exception. An example is a global exception class such as ArgumentException. Callers should be able to assume that there are no side effects when an exception is thrown from a method. For example, if you have code that transfers money by withdrawing from one account and depositing in another account, and an exception is thrown while executing the deposit, you don't want the withdrawal to remain in effect.
The method above does not directly throw any exceptions, but must be written defensively so that if the deposit operation fails, the withdrawal is reversed.
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