Assertation Error
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which case should I throw it from my own code? up vote 24 down vote favorite 5 In Item 2 of the "Effective Java, 2nd edition" book, there is this snippet of code, in which the author wants to forbid the empty initialization of an object. class Example { private Example() { throw new AssertionError(); } } The type of exception thrown, is what confuses me assertion error stateflow here. I don't understand if the AssertionError is thrown just because of an absence of more suited errors or because it should be this way. As I understand, this error is thrown by the framework when an assert statement fails. Also, in the javadoc it's just written [An AssertionError is] Thrown to indicate that an assertion has failed. But I don't see any assertion (true-false statement) being violated here. Of course the "You shall not instantiate an item of this class" statement has been violated, but if this is the logic behind that, then we should all throw AssertionErrors everywhere, and that is obviously not what happens. FWIW, I'd have just thrown a new IllegalStateException("Must not instantiate an element of this class") Is there something wrong with that? In which case should I throw an AssertionError in my own code? Sorry if it's just a subtle doubt but I use this pattern a lot in my code and I want to make sure I'm doing the right thing. java exception effective-java share|improve this question edited Jul 21 '14 at 11:03 asked Jul 21 '14 at 10:43 doplumi 88721131 1 "Assertions" doesn't just mean "assert
think about how the code works. Or an assertion could document a constraint on the system. (See also: ExceptionsAsConstraints) However, it is often possible to actually compile the assertion to code assertion error in java and let it be executed in context to see if the statement it makes really assertion error processing does hold. When programmers talk about assertions they usually mean this kind of executed assertion. Standard CeeCeePlusPlus provides the "assert" macro, which assertion error in java example looks just like a function call. Here's a simple example: assert(0 <= index && index < length); As long as the index is within the range specified, this statement is a no-op. If the index is out http://stackoverflow.com/questions/24863185/what-is-an-assertionerror-in-which-case-should-i-throw-it-from-my-own-code of range, however, the assertion will terminate the application and (ideally) display the failed boolean expression "0 <= index && index < length" as well as the filename and line number of the assertion in the source code. The diagnostic information printed by a failed assertion (not to mention the potentially dramatic act of terminating the offending program) is obviously not very end-user friendly. This goes to an important point: assertions are not an error-handling http://c2.com/cgi/wiki?WhatAreAssertions mechanism. The purpose of an assertion is not to handle an error, it is to (ultimately) notify a programmer of an error so that he can fix it. Since assertions that don't fail are no-ops, once a program has been thoroughly tested and bug-fixed, it is possible to recompile the source code without the assertions to produce a program that is both smaller and faster; for programs that make heavy use of assertions, this can result in an appreciable difference in performance. In C, this can be accomplished simply by making sure the NDEBUG macro is defined before all inclusions of the
This Site Careers Other all forums Forum: Java in General Right way to deal with AssertionError Jaikiran Pai Marshal Posts: 10447 227 I like... posted 10 years ago Hi, We have a production level application, which we are trying to integrate with a different module. One https://coderanch.com/t/378973/java/java/deal-AssertionError of the issues that we are running into is that the code in the module, has 'asserts'. Now, because of this there are quite a few occasions when we have seen the java.lang.AssertionError being thrown. Our problem is that in our application, we are catching java.lang.Exception and on catching the exception, we do some additional logic. Now, since the AssertionError extends from Throwable, this never gets caught and we are not seeing the expected behaviour in our assertion error application. My question is, Is it a right practice to throw AssertionError in production level code. Are applications supposed to catch them? I wanted to know this so that we can either change the code in the module that we are integrating our application with, or just start catching Throwable instead of Exception in our application, so that even the AssertionError is caught. Thank you. [My Blog] [JavaRanch Journal] Ernest Friedman-Hill author and iconoclast Marshal Posts: 24212 assertion error in 35 I like... posted 10 years ago AssertionErrors are thrown when assertions fail. Assertions fail because something the programmer believed to be true turns out not to be true. That means there is a bug in the code. If you see an AssertionError, find and fix the source of the problem right away! If you catch an AssertionError and continue, then you have no idea whether the application is working correctly anymore. From that point forward, it's entirely possible that everything the application does is garbage. [Jess in Action][AskingGoodQuestions] Jesper de Jong Java Cowboy Saloon Keeper Posts: 15495 43 I like... posted 10 years ago Do you know exactly what assertions are and what they are used for? An example of the use of assertions is to check pre- and postconditions in parts of your code. A method may for example have an assert to check that the parameters that were passed to it are valid. If an AssertionError happens in your application, it means that there is a bug somewhere in your software. You might be passing invalid arguments to a method somewhere, or you're doing something else so that the software gets into an undefined, invalid state. AssertionErrors should NEVER happen in production software. If an AssertionError happens, it means that something is seriously wrong in your software and you should debug it. Java Beginners FAQ - JavaRan