Error In Constructor
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Error Injecting Constructor
Sheppy ethertank Nickolay evilpie trevorh teoli davidbourguignon secoif DomenicDenicola dgchurchill timemachine3030 Sevenspade Potappo Sephr Brettz9 Mgjbot Allanbonadio Ptak82 JustinLudwig Error In This Article SyntaxParametersDescriptionError typesPropertiesMethodsError instancesPropertiesStandard propertiesVendor-specific extensionsMicrosoftMozillaMethodsExamplesThrowing a generic errorHandling a specific errorCustom Error TypesSpecificationsBrowser compatibilitySee also The Error constructor creates an error object. Instances of Error objects are thrown when runtime errors occur. The Error object can also be used as a base object for user-defined exceptions. See below for standard built-in error types. Syntax new Error([message[, fileName[, lineNumber]]]) Parameters message Optional. Human-readable description of the error. fileName Optional. The value for the fileName property on the created Error object. Defaults to the name of the file containing the code that called the Error() constructor. lineNumber Optional. The value for the lineNumber property on the created Error object. Defaults to the line number containing the Error() constructor invocation. Description Runtime error
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Error Injecting Constructor Org.apache.lucene.store.lockobtainfailedexception Lock Obtain Timed Out
site About Us Learn more about Stack Overflow the company Business Learn more error injecting constructor java.lang.nosuchfielderror static_dir about hiring developers or posting ads with us Programmers Questions Tags Users Badges Unanswered Ask Question _ Programmers Stack c++ constructor error handling Exchange is a question and answer site for professional programmers interested in conceptual questions about software development. Join them; it only takes a minute: Sign up Here's how it works: Anybody can https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Error ask a question Anybody can answer The best answers are voted up and rise to the top How to write constructors which might fail to properly instantiate an object up vote 8 down vote favorite 2 Sometimes you need to write a constructor which can fail. For instance, say I want to instantiate an object with a file path, something like obj = http://programmers.stackexchange.com/questions/60250/how-to-write-constructors-which-might-fail-to-properly-instantiate-an-object new Object("/home/user/foo_file") As long as the path points to an appropriate file everything's fine. But if the string is not a valid path things should break. But how? You could: throw an exception return null object (if your programming language allows constructors to return values) return a valid object but with a flag indicating that its path wasn't set properly (ugh) others? I assume that the "best practices" of various programming languages would implement this differently. For instance I think ObjC prefers (2). But (2) would be impossible to implement in C++ where constructors must have void as a return type. In that case I take it that (1) is used. In your programming language of choice can you show how you'd handle this problem and explain why? constructors initialization share|improve this question edited Dec 21 '15 at 21:13 gnat 21.8k1365129 asked Mar 20 '11 at 19:24 whitman 143113 1 Exceptions in Java are one way of handling this. –Mahmoud Hossam Mar 20 '11 at 19:29 C++ constructors don't return void - they return an object. –gablin Mar 20 '11 at 20:59 5 @gablin: Actua
when I was learning C++, this is the kind of summary that I would have liked to read. So here it is, for the happy few! In C++ there are two common idioms https://blog.barthe.ph/2009/08/28/cpp_object_init_and_errors/ with regards to object construction and initialization. the constructor fully initializes the object: this http://speakingjs.com/es5/ch14.html idiom makes it impossible to construct an object which is not correctly initialized and ready to use. the constructor does not initialize (or partially initialize) the object: the initialization is performed at a latter stage by calling some init() method. This, in effect, splits the object allocation and initialization. It is common to encounter this pattern whenever error in the class mimics some transactional behavior like opening/closing a file, connection/disconnecting from a server… One may have legitimate reasons to use one idiom rather than the other, but as a rule of thumb the first approach (full initialization in constructor) should be favored. This is because it makes it hard to use the interface of the object incorrectly. In the second case it is possible to construct the object and error injecting constructor call a method on it before the initialization was performed. There are two ways to handle this improper usage: do nothing and state that this is an “undefined behavior”. It will probably make the class a bit faster to write, but harder to debug. Not a good idea… carry an internal state to remember whether or not the object was initialized. This make it possible to report errors in a much more graceful way. On the other hand it puts the burden on maintaining an internal state and checking against it. Maintaining an internal state looks very easy but my experience is that it is error prone in the long run… So in summary, unless you have a good reason not to construct a fully initialized object, then you should. It will make your code harder to use incorrectly and much simpler. And you probably will have to write less. There’s one issue though… Error handling. There are three general ways to handle errors: exceptions: this is the recommended and the best possible way. return error code on each function: this is the classical C idiom. In practice it means every function you call returns an error code and that you MUST! check against it. global error state: there i
what exception handling is.What Is Exception Handling?In exception handling, you often group statements that are tightly coupled. If, while you are executing those statements, one of them causes an error, then it makes no sense to continue with the remaining statements. Instead, you try to recover from the error as gracefully as you can. This is loosely reminiscent of transactions (but without the atomicity).Let’s look at code without exception handling:function processFiles() { var fileNames = collectFileNames(); var entries = extractAllEntries(fileNames); processEntries(entries); } function extractAllEntries(fileNames) { var allEntries = new Entries(); fileNames.forEach(function (fileName) { var entry = extractOneEntry(fileName); allEntries.add(entry); // (1) }); } function extractOneEntry(fileName) { var file = openFile(fileName); // (2) ... } ...What is the best way to react to an error in openFile() at (2)? Clearly, the statement (1) should not be executed anymore. But we wouldn’t want to abort extractAllEntries(), either. Instead, it is enough to skip the current file and continue with the next one. To do that, we add exception handling to the previous code:function extractAllEntries(fileNames) { var allEntries = new Entries(); fileNames.forEach(function (fileName) { try { var entry = extractOneEntry(fileName); allEntries.add(entry); } catch (exception) { // (2) errorLog.log('Error in '+fileName, exception); } }); } function extractOneEntry(fileName) { var file = openFile(fileName); ... } function openFile(fileName) { if (!exists(fileName)) { throw new Error('Could not find file '+fileName); // (1) } ... }There are two aspects to exception handling: If there is a problem that can’t be handled meaningfully where it occurs, throw an exception. Find a place where errors can be handled: catch exceptions. At (1), the following constructs are active: processFile() extractAllEntries(...) fileNames.forEach(...) function (fileName) { ... } try { ... } catch (exception) { ... } extractOneEntry(...) openFile(...)The throw statement at (1) walks up that tree and leaves all constructs until it encounters an active try statement. It then invokes that statement’s catch block and passes it the exception value.Exception Handling in JavaScriptException handling in JavaScript works like in most programming languages: a try statement groups statements and lets you intercept exceptions in those statements.throwThe syntax of throw is as follows:throw «value»;Any JavaScript value can be thrown. For simplicity’s sake, many Jav