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Java Forum / General / February 2007which exception?
Hi, which is the right exception to manage an "out of memory situation" when I create an object with the new operator? try { Time t = new Time(); }catch(...) { //////// out of memory } Thanks josh schrieb: > Hi, > > which is the right exception to manage an "out of memory situation" > when I create an object with the new operator? If the system runs out of memory, an OutOfMemoryError is thrown. An Error (java.lang.Error) is not an Exception and therefore should not be caught. Bye Michael > josh schrieb: > [quoted text clipped - 9 lines] > Bye > Michael My problem is to convert C++ code like this: Time *t; try { t = new Time(15,10,00); } catch(bad_alloc ba) { cout << "OUT OF MEMORY!!\n"; return EXIT_FAILURE; } so how I can do that? > My problem is to convert C++ code like this: > [quoted text clipped - 11 lines] > > so how I can do that? It's easy: don't mind the "out of memory situation". The Java equivalent would be: Time t = new Time(15,10,00); There is a distinction in Java between Errors and Exceptions (both are subtypes of java.lang.Throwable). Errors indicates conditions where it doesn't make (much) sense to handle them - more: the documentation says that one should not handle them. Bye Michael > My problem is to convert C++ code like this: > [quoted text clipped - 11 lines] > > so how I can do that? Time t = new Time( 15, 10, 00 ); If it runs out of memory, an error is thrown and the program will terminate, just as the C++ does. (Unless there's an outer shell that catches and handles it, of course, which in principle there /could/ be. But then, you shouldn't try and second-guess that.)  SignatureChris "electric hedgehog" Dollin "It's just the beginning we've seen" - Colosseum, /Tomorrow's Blues/ >> try >> { [quoted text clipped - 12 lines] > If it runs out of memory, an error is thrown and the program will > terminate, just as the C++ does. Duh. Somehow I read an `exit(EXIT_FAILURE)` rather than a `return` up there. Today, I'm an idiot. Ignore my previous post. SignatureChris "electric idiot" Dollin There' no hortage of vowel on Uenet. > >> try > >> { [quoted text clipped - 19 lines] > Chris "electric idiot" Dollin > There' no hortage of vowel on Uenet. In C++, I thought the "new" operator returned NULL if there wasn't enough memory... In any case, The concerns of Memory management are different in Java than in C++. Don't try to "handle" out of memory exceptions, as they generally imply a bug, rather than a true resource limitation. > My problem is to convert C++ code like this: > [quoted text clipped - 9 lines] > return EXIT_FAILURE; > } The API implied by the C++ code fragment is not suitable for use in Java. Normally it is a bad idea to return error status for exeptional conditions, exceptions are intended to be used in such circumstances. So, a first approximation to that code (in Java) would be try { t = new Time(15,10,00); } catch (/* what goes here ??*/) { system.err.println("Out of Memory !!"); throw new MyOutOfMemoryException(); } But that has some problems -- it's not likely that you'd be able to write to system.err if the program was out of memory, for one (though there /might/ be more sophisticated ways of dealing with the problem which /did/ allow the program to carry on). So, we might have try { t = new Time(15,10,00); } catch (/* what goes here ??*/) { throw new MyOutOfMemoryException(); } But that, for most purposes is redundant, since the exeption that the system throwns (OutOfMemoryError) is sufficient on its own. So we can remove both the catch and the throw: t = new Time(15,10,00); Or -- if you've managed to find a way to allow your program to continue after an OOME (not easy) -- then you might have try { t = new Time(15,10,00); } catch (OutOfMemoryError e) { invokeCleverRecoveryCode(); throw new MyOperationFailedException(e); } But that would be pretty unusual.... -- chris > try > { [quoted text clipped - 5 lines] > return EXIT_FAILURE; > } Not necessarily "out of memory", but "out of free chunks of contigous memory the size of the object". Java manages the memory - there is a reason people write virtual memory/garbage collection systems for C++ programmers. So just don't worry about it. ... > which is the right exception to manage an "out of memory situation" > when I create an object with the new operator? 'That does not happen.' Or rather, it would be exceptional for it to happen on the creation of 'a single object' as suggested in the code snippet. It might happen after creating 100's of thousands, or millions of average objects, but the JVM can work with astonishing amounts of data before hitting memory problems, even with the default memory size. Much more common in this situation, is that the application has a memory leak. I sughgest you prepare an SSCCE*, and if that fails to reveal the problem, post it here. * <http://www.physci.org/codes/sscce> In addition to what Michael was mentioning, I will add that although Error's should generally not be caught, an OOME *can* be caught, and with a little preparation, it is possible to show the end user an 'Error' dialog (at least) before the program shuts down. But look into the SSCCE first. Andrew T. > which is the right exception to manage an "out of memory situation" > when I create an object with the new operator? If the constructor fails, an appropriate exception will be raised. Why do you want to replace it with a different one, especially if you don't know which what you want to replace it with? /gordon Signature[ don't email me support questions or followups ] g o r d o n + n e w s @ b a l d e r 1 3 . s e > If the constructor fails, an appropriate exception will be raised. what? If I didn't want a generic Exception josh schreef: >> If the constructor fails, an appropriate exception will be raised. > > what? If I didn't want a generic Exception It is not a generic Exception. It is an ‘appropriate exception’. In this case, even an Error: OutOfMemoryError H. - -- Hendrik Maryns http://tcl.sfs.uni-tuebingen.de/~hendrik/ ================== http://aouw.org Ask smart questions, get good answers: http://www.catb.org/~esr/faqs/smart-questions.html Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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