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  • New/strange Java "try()" syntax?

    - by Ali
    While messing around with the custom formatting options in Eclipse, in one of the sample pieces of code, I say code as follows: /** * 'try-with-resources' */ class Example { void foo() { try (FileReader reader1 = new FileReader("file1"); FileReader reader2 = new FileReader("file2")) { } } } I've never seen try used like this and I've been coding in Java for 9 years! Does any one know why you would do this? What is a possible use-case / benefit of doing this? An other pieces of code I saw, I thought was a very useful shorthand so I'm sharing it here as well, it's pretty obvious what it does: /** * 'multi-catch' */ class Example { void foo() { try { } catch (IllegalArgumentException | NullPointerException | ClassCastException e) { e.printStackTrace(); } } }

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  • Thoughts on try-catch blocks

    - by John Boker
    What are your thoughts on code that looks like this: public void doSomething() { try { // actual code goes here } catch (Exception ex) { throw; } } The problem I see is the actual error is not handled, just throwing the exception in a different place. I find it more difficult to debug because i don't get a line number where the actual problem is. So my question is why would this be good? ---- EDIT ---- From the answers it looks like most people are saying it's pointless to do this with no custom or specific exceptions being caught. That's what i wanted comments on, when no specific exception is being caught. I can see the point of actually doing something with a caught exception, just not the way this code is.

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  • Enclosing service execution in try-catch: bad practice?

    - by Sorin Comanescu
    Hi, Below is the usual Program.cs content for a windows service program: static class Program { /// <summary> /// The main entry point for the application. /// </summary> static void Main() { ServiceBase[] ServicesToRun; ServicesToRun = new ServiceBase[] { new MyService() }; ServiceBase.Run(ServicesToRun); } } Is it a bad practice to enclose the ServiceBase.Run(...) in a try-catch block? Thanks.

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  • Enclosing service execution in try-catch

    - by Sorin Comanescu
    Hi, Below is the usual Program.cs content for a windows service program: static class Program { /// <summary> /// The main entry point for the application. /// </summary> static void Main() { ServiceBase[] ServicesToRun; ServicesToRun = new ServiceBase[] { new MyService() }; ServiceBase.Run(ServicesToRun); } } Is it a bad practice to enclose the ServiceBase.Run(...) in a try-catch block? Thanks.

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  • Catching an exception that is nested into another exception

    - by Bernhard V
    Hi, I want to catch an exception, that is nested into another exception. I'm doing it currently this way: } catch (RemoteAccessException e) { if (e != null && e.getCause() != null && e.getCause().getCause() != null) { MyException etrp = (MyException) e.getCause().getCause(); ... } else { throw new IllegalStateException("Error at calling service 'beitragskontonrVerwalten'"); } } Is there a way to do this more efficient and elegant?

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  • Catch test case order [on hold]

    - by DeadMG
    Can I guarantee the order of execution with multiple TEST_CASEs with Catch? I am testing some code using LLVM, and they have some despicable global state that I need to explicitly initialize. Right now I have one test case that's like this: TEST_CASE("", "") { // Initialize really shitty LLVM global variables. llvm::InitializeAllTargets(); llvm::InitializeAllTargetMCs(); llvm::InitializeAllAsmPrinters(); llvm::InitializeNativeTarget(); llvm::InitializeAllAsmParsers(); // Some per-test setup I can make into its own function CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile(...)); CHECK_NOTHROW(Compile...)); CHECK_NOTHROW(Interpret(...)); CHECK_THROWS(Compile(...)); CHECK_THROWS(Compile(...)); } What I want is to refactor it into three TEST_CASE, one for tests that should pass compilation, one for tests that should fail, and -one for tests that should pass interpretation (and in the future, further such divisions, perhaps). But I can't simply move the test contents into another TEST_CASE because if that TEST_CASE is called before the one that sets up the inconvenient globals, then they won't be initialized and the testing will spuriously fail.

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  • clear explanation sought: throw() and stack unwinding

    - by Jerry Gagelman
    I'm not a programmer but have learned a lot watching others. I am writing wrapper classes to simplify things with a really technical API that I'm working with. Its routines return error codes, and I have a function that converts those to strings: static const char* LibErrString(int errno); For uniformity I decided to have member of my classes throw an exception when an error is encountered. I created a class: struct MyExcept : public std::exception { const char* errstr_; const char* what() const throw() {return errstr_;} MyExcept(const char* errstr) : errstr_(errstr) {} }; Then, in one of my classes: class Foo { public: void bar() { int err = SomeAPIRoutine(...); if (err != SUCCESS) throw MyExcept(LibErrString(err)); // otherwise... } }; The whole thing works perfectly: if SomeAPIRoutine returns an error, a try-catch block around the call to Foo::bar catches a standard exception with the correct error string in what(). Then I wanted the member to give more information: void Foo::bar() { char adieu[128]; int err = SomeAPIRoutine(...); if (err != SUCCESS) { std::strcpy(adieu,"In Foo::bar... "); std::strcat(adieu,LibErrString(err)); throw MyExcept((const char*)adieu); } // otherwise... } However, when SomeAPIRoutine returns an error, the what() string returned by the exception contains only garbage. It occurred to me that the problem could be due to adieu going out of scope once the throw is called. I changed the code by moving adieu out of the member definition and making it an attribute of the class Foo. After this, the whole thing worked perfectly: a try-call block around a call to Foo::bar that catches an exception has the correct (expanded) string in what(). Finally, my question: what exactly is popped off the stack (in sequence) when the exception is thrown in the if-block when the stack "unwinds?" As I mentioned above, I'm a mathematician, not a programmer. I could use a really lucid explanation of what goes onto the stack (in sequence) when this C++ gets converted into running machine code.

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  • Try/Catch or test parameters

    - by Ondra Morský
    I was recently on a job interview and I was given a task to write simple method in C# to calculate when the trains meet. The code was simple mathematical equation. What I did was that I checked all the parameters on the beginning of the method to make sure, that the code will not fail. My question is: Is it better to check the parameters, or use try/catch? Here are my thoughts: Try/catch is shorter Try/catch will work always even if you forget about some condition Catch is slow in .NET Testing parameters is probably cleaner code (Exceptions should be exceptional) Testing parameters gives you more control over return values I would prefer testing parameters in methods longer than +/- 10 lines, but what do you think about using try/catch in simple methods just like this – i.e. return (a*b)/(c+d); There are many similar questions on stackexchnage, but I am interested in this particular scenario.

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  • Why doesn't Perl's Try::Tiny's try/catch give me the same results as eval?

    - by sid_com
    Why doesn't the subroutine with try/catch give me the same results as the eval-version does? #!/usr/bin/env perl use warnings; use strict; use 5.012; use Try::Tiny; sub shell_command_1 { my $command = shift; my $timeout_alarm = shift; my @array; eval { local $SIG{ALRM} = sub { die "timeout '$command'\n" }; alarm $timeout_alarm; @array = qx( $command ); alarm 0; }; die $@ if $@ && $@ ne "timeout '$command'\n"; warn $@ if $@ && $@ eq "timeout '$command'\n"; return @array; } shell_command_1( 'sleep 4', 3 ); say "Test_1"; sub shell_command_2 { my $command = shift; my $timeout_alarm = shift; my @array; try { local $SIG{ALRM} = sub { die "timeout '$command'\n" }; alarm $timeout_alarm; @array = qx( $command ); alarm 0; } catch { die $_ if $_ ne "timeout '$command'\n"; warn $_ if $_ eq "timeout '$command'\n"; } return @array; } shell_command_2( 'sleep 4', 3 ); say "Test_2"

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  • Java try finally variations

    - by Petr Gladkikh
    This question nags me for a while but I did not found complete answer to it yet (e.g. this one is for C# http://stackoverflow.com/questions/463029/initializing-disposable-resources-outside-or-inside-try-finally). Consider two following Java code fragments: Closeable in = new FileInputStream("data.txt"); try { doSomething(in); } finally { in.close(); } and second variation Closeable in = null; try { in = new FileInputStream("data.txt"); doSomething(in); } finally { if (null != in) in.close(); } The part that worries me is that the thread might be somewhat interrupted between the moment resource is acquired (e.g. file is opened) but resulting value is not assigned to respective local variable. Is there any other scenarios the thread might be interrupted in the point above other than: InterruptedException (e.g. via Thread#interrupt()) or OutOfMemoryError exception is thrown JVM exits (e.g. via kill, System.exit()) Hardware fail (or bug in JVM for complete list :) I have read that second approach is somewhat more "idiomatic" but IMO in the scenario above there's no difference and in all other scenarios they are equal. So the question: What are the differences between the two? Which should I prefer if I do concerned about freeing resources (especially in heavily multi-threading applications)? Why? I would appreciate if anyone points me to parts of Java/JVM specs that support the answers.

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  • Try::Tiny-Question

    - by sid_com
    Why doesn't the subroutine with try/catch give me the same results as the eval-version does. #!/usr/bin/env perl use warnings; use strict; use 5.012; use Try::Tiny; sub shell_command_1 { my $command = shift; my $timeout_alarm = shift; my @array; eval { local $SIG{ALRM} = sub { die "timeout '$command'\n" }; alarm $timeout_alarm; @array = qx( $command ); alarm 0; }; die $@ if $@ && $@ ne "timeout '$command'\n"; warn $@ if $@ && $@ eq "timeout '$command'\n"; return @array; } shell_command_1( 'sleep 4', 3 ); say "Test_1"; sub shell_command_2 { my $command = shift; my $timeout_alarm = shift; my @array; try { local $SIG{ALRM} = sub { die "timeout '$command'\n" }; alarm $timeout_alarm; @array = qx( $command ); alarm 0; } catch { die $_ if $_ ne "timeout '$command'\n"; warn $_ if $_ eq "timeout '$command'\n"; } return @array; } shell_command_2( 'sleep 4', 3 ); say "Test_2"

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  • Can/Should you throw exceptions in a c# switch statement?

    - by Kettenbach
    Hi All, I have an insert query that returns an int. Based on that int I may wish to throw an exception. Is this appropriate to do within a switch statement? switch (result) { case D_USER_NOT_FOUND: throw new ClientException(string.Format("D User Name: {0} , was not found.", dTbx.Text)); case C_USER_NOT_FOUND: throw new ClientException(string.Format("C User Name: {0} , was not found.", cTbx.Text)); case D_USER_ALREADY_MAPPED: throw new ClientException(string.Format("D User Name: {0} , is already mapped.", dTbx.Text)); case C_USER_ALREADY_MAPPED: throw new ClientException(string.Format("C User Name: {0} , is already mapped.", cTbx.Text)); default: break; } I normally add break statements to switches but they will not be hit. Is this a bad design? Please share any opinions/suggestions with me. Thanks, ~ck in San Diego

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  • Throw a long list of exceptions vs throw an Exception vs throw custom exception?

    - by athena
    I have an application which uses two methods of an API. Both these methods throw more than five exceptions each. So, if I just add a throws declaration then it becomes a list of more than ten. (My method cannot handle any of the ten exceptions) I have read that throwing a long list of exceptions is a bad practice. Also throwing (the umbrella) Exception is a bad practice. So, what should I do? Add a try catch block, and log and exit in the catch block? (Current approach) Create a custom exception class, wrap every exception and throw the custom exception? Add a throws declaration for all exceptions? Throw Exception?

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  • SQL SERVER – Convert Old Syntax of RAISEERROR to THROW

    - by Pinal Dave
    I have been quite a few comments on my Facebook page and here is one of the questions which instantly caught my attention. “We have a legacy application and it has been a long time since we are using SQL Server. Recently we have upgraded to the latest version of SQL Server and we are updating our code as well. Here is the question for you, there are plenty of places we have been using old style RAISEERROR code and now we want to convert it to use THROW. Would you please suggest a sample example for the same.” Very interesting question. THROW was introduced in SQL Server 2012 to handle the error gracefully and return the error message. Let us see quickly two examples of SQL Server 2012 and earlier version. Earlier Version of SQL Server BEGIN TRY SELECT 1/0 END TRY BEGIN CATCH DECLARE @ErrorMessage NVARCHAR(2000), @ErrorSeverity INT SELECT @ErrorMessage = ERROR_MESSAGE(), @ErrorSeverity = ERROR_SEVERITY() RAISERROR (@ErrorMessage, @ErrorSeverity, 1) END CATCH SQL Server 2012 and Latest Version BEGIN TRY SELECT 1/0 END TRY BEGIN CATCH THROW END CATCH That’s it! We are done! Reference: Pinal Dave (http://blog.SQLAuthority.com)Filed under: PostADay, SQL, SQL Authority, SQL Error Messages, SQL Query, SQL Server, SQL Tips and Tricks, T SQL

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  • Is your TRY worth catching?

    - by Maria Zakourdaev
      A very useful error handling TRY/CATCH construct is widely used to catch all execution errors  that do not close the database connection. The biggest downside is that in the case of multiple errors the TRY/CATCH mechanism will only catch the last error. An example of this can be seen during a standard restore operation. In this example I attempt to perform a restore from a file that no longer exists. Two errors are being fired: 3201 and 3013: Assuming that we are using the TRY and CATCH construct, the ERROR_MESSAGE() function will catch the last message only: To workaround this problem you can prepare a temporary table that will receive the statement output. Execute the statement inside the xp_cmdshell stored procedure, connect back to the SQL Server using the command line utility sqlcmd and redirect it's output into the previously created temp table.  After receiving the output, you will need to parse it to understand whether the statement has finished successfully or failed. It’s quite easy to accomplish as long as you know which statement was executed. In the case of generic executions you can query the output table and search for words like“Msg%Level%State%” that are usually a part of the error message.Furthermore, you don’t need TRY/CATCH in the above workaround, since the xp_cmdshell procedure always finishes successfully and you can decide whether to fire the RAISERROR statement or not. Yours, Maria

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  • I can't boot into Ubuntu "Try (hd0,0): NTFS5: No ang0" Error Message

    - by Joe
    I recently installed Ubuntu 12.04 alongside windows 7. It was working fine but now when I try to boot with ubuntu after the operating system choice screen I get this. Boot Error Message Try (hd0,0): NFTS5: No ang0 Try (hd0,1): NTFS5: No ang0 Try (hd0,2): NTFS5: No ang0 Try (hd0,3): Extended: Try (hd0,4): NTFS5: No ang0 Try (hd0,5): Extended: Try (hd0,5): EXT2: And when I press ctrl+alt+del it restarts the computer and if I chose to boot with ubuntu same thing happens again. But windows works fine.. How do I resolve this problem? Thanks.

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  • Why can't I write just a try with no catch or finally?

    - by Camilo Martin
    Sometimes I do this and I've seen others doing it too: VB: Try DontWannaCatchIt() Catch End Try C#: try { DontWannaCatchIt(); } catch {} I know I should catch every important exception and do something about it, but sometimes it's not important to - or am I doing something wrong? Is this usage of the try block incorrect, and the requirement of at least one catch or finally block an indication of it?

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  • Validating data to nest if or not within try and catch

    - by Skippy
    I am validating data, in this case I want one of three ints. I am asking this question, as it is the fundamental principle I'm interested in. This is a basic example, but I am developing best practices now, so when things become more complicated later, I am better equipped to manage them. Is it preferable to have the try and catch followed by the condition: public static int getProcType() { try { procType = getIntInput("Enter procedure type -\n" + " 1 for Exploratory,\n" + " 2 for Reconstructive, \n" + "3 for Follow up: \n"); } catch (NumberFormatException ex) { System.out.println("Error! Enter a valid option!"); getProcType(); } if (procType == 1 || procType == 2 || procType == 3) { hrlyRate = hrlyRate(procType); procedure = procedure(procType); } else { System.out.println("Error! Enter a valid option!"); getProcType(); } return procType; } Or is it better to put the if within the try and catch? public static int getProcType() { try { procType = getIntInput("Enter procedure type -\n" + " 1 for Exploratory,\n" + " 2 for Reconstructive, \n" + "3 for Follow up: \n"); if (procType == 1 || procType == 2 || procType == 3) { hrlyRate = hrlyRate(procType); procedure = procedure(procType); } else { System.out.println("Error! Enter a valid option!"); getProcType(); } } catch (NumberFormatException ex) { System.out.println("Error! Enter a valid option!"); getProcType(); } return procType; } I am thinking the if within the try, may be quicker, but also may be clumsy. Which would be better, as my programming becomes more advanced?

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  • PowerShell Try Catch Finally

    - by PointsToShare
    PowerShell Try Catch Finally I am a relative novice to PowerShell and tried (pun intended) to use the “Try Catch Finally” in my scripts. Alas the structure that we love and use in C# (or even – shudder of shudders - in VB) does not always work in PowerShell. It turns out that it works only when the error is a terminating error (whatever that means). Well, you can turn all your errors to the terminating kind by simply setting - $ErrorActionPreference = "Stop", And later resetting it back to “Continue”, which is its normal setting. Now, the lazy approach is to start all your scripts with: $ErrorActionPreference = "Stop" And ending all of them with: $ErrorActionPreference = "Continue" But this opens you to trouble because should your script have an error that you neglected to catch (it even happens to me!), your session will now have all its errors as “terminating”. Obviously this is not a good thing, so instead let’s put these two setups in the beginning of each Try block and in the Finally block as seen below: That’s All Folks!!

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  • Zend - unable to catch exception [closed]

    - by coder3
    This still throw an uncaught exception.. Any insight why this isn't working? protected function login() { $cart = $this->getHelper('GetCurrentCart'); $returnValue = false; if ($this->view->form->isValid($this->_getAllParams())) { $values = $this->view->form->getValues(); try { $this->goreg = $this->goregFactory->create($this->config->goreg->service_url); if ($this->goreg->login($values['username'], $values['password']) && $this->goregSession->isLoggedIn()) { $returnValue = true; } else { echo 'success 1'; } } catch (Exception $e) { echo 'error 1'; } catch (Zend_Exception $e) { echo 'error 2'; } catch (Zend_Http_Client_Exception $e) { echo 'error 3'; } } return $returnValue; }

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  • SQL Server Begin Try

    - by Derek Dieter
    The try catch methodology of programming is a great innovation for SQL 2005+. The first question you should ask yourself before using Try/Catch should be “why?”. Why am I going to use Try/Catch? Personally, I have found a few uses, however I must say I do fall into the category of not [...]

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  • Build one to throw away vs Second-system effect

    - by m3th0dman
    One one hand there is an advice that says "Build one to throw away". Only after finishing a software system and seeing the end product we realize what went wrong in the design phase and understand how we should have really done it. On the other hand there is the "second-system effect" which says that the second system of the same kind that is designed is usually worse than the first one; there are many features that did not fit in the first project and were pushed into the second version usually leading to overly complex and overly engineered. Isn't here some contradiction between these principles? What is the correct view over the problems and where is the border between these two? I believe that these "good practices" are were firstly promoted in the seminal book The Mythical Man-Month by Fred Brooks. I know that some of these issues are solved by Agile methodologies, but deep down, the problem is still the principles still stand; for example we would not make important design changes 3 sprints before going live.

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