What happens if a checked exception is never caught

When interfaces are involved, more than one method declaration may be overridden by a single overriding declaration. We say that a statement or expression can throw a checked exception type E if, according to the rules given below, the execution of the statement or expression can result in an exception of type E being thrown.

Identifier and the Primary expression can throw E ; or Some expression of the argument list can throw E ; or E is listed in the throws clause of the type of method that is invoked. A class instance creation expression can throw an exception type E iff either: The expression is a qualified class instance creation expression and the qualifying expression can throw E ; or Some expression of the argument list can throw E ; or E is listed in the throws clause of the type of the constructor that is invoked; or The class instance creation expression includes a ClassBody , and some instnance initializer block or instance variable initializer expression in the ClassBody can throw E.

For every other kind of expression, the expression can throw type E iff one of its immediate subexpressions can throw E. An explicit constructor invocation statement can throw an exception type E iff either: Some subexpression of the constructor invocation's parameter list can throw E ; or E is declared in the throws clause of the constructor that is invoked. A try statement can throw an exception type E iff either: The try block can throw E and E is not assignable to any catch parameter of the try statement and either no finally block is present or the finally block can complete normally; or Some catch block of the try statement can throw E and either no finally block is present or the finally block can complete normally; or A finally block is present and can throw E.

Any other statement S can throw an exception type E iff an expression or statement immediately contained in S can throw E. It is compile-time error if an instance variable initializer of a named class can throw a checked exception unless that exception or one of its supertypes is explicitly declared in the throws clause of each constructor of its class and the class has at least one explicitly declared constructor.

A program declaring such exceptions would be cluttered, pointlessly. Many of the operations and constructs of the Java programming language can result in runtime exceptions. The information available to a compiler, and the level of analysis the compiler performs, are usually not sufficient to establish that such run-time exceptions cannot occur, even though this may be obvious to the programmer.

Requiring such exception classes to be declared would simply be an irritation to programmers. For example, certain code might implement a circular data structure that, by construction, can never involve null references; the programmer can then be certain that a NullPointerException cannot occur, but it would be difficult for a compiler to prove it.

The theorem-proving technology that is needed to establish such global properties of data structures is beyond the scope of this specification.

That said, I've rarely seen InterruptedException handled properly! One more thing - a RuntimeException is not always "where a developer got something wrong". An illegal argument exception is thrown when you try and create an enum using valueOf and there's no enum of that name.

This is not necessarily a mistake by the developer! A problem with checked exceptions is that exceptions are often attached to methods of an interface if even one implementation of that interface uses it. Another problem with checked exceptions is that they tend to be misused.

The perfect example of this is in java. Connection 's close method. It can throw a SQLException , even though you've already explicitly stated that you're done with the Connection. What information could close possibly convey that you'd care about? Also, don't get me started on the various parse methods and NumberFormatException Checked exceptions were, in their original form, an attempt to handle contingencies rather than failures.

These failures were never correct to be declared as checked exceptions. If our application is not a DB.. That would violate the principle of encapsulation. The other severe flaw in the Java design, was that exception-handling should correctly placed at the highest possible "business" or "request" level.

The principle here is "throw early, catch late". Checked exceptions do little but get in the way of this. Almost none of these implement any genuine handling or reliability, but impose major coding overhead.

Many people talk about "handling" checked exceptions, but are talking through their hats. Continuing after a failure with null, incomplete or incorrect data to pretend success is not handling anything. Failing cleanly, is the most basic correct strategy for handling an exception. Other strategies for exception-handling are "retry", "reconnect" or "skip", at the business, subsystem, or request level. Lastly, it is far preferable to fail, than to run with incorrect data.

People get fired for that. The programmer needs to know all of the exceptions that a method may throw, in order to use it correctly. So, beating him over the head with just some of the exceptions does not necessarily help a careless programmer avoid errors. The slim benefit is outweighed by the burdensome cost especially in larger, less flexible code bases where constantly modifying the interface signatures is not practical.

Static analysis can be nice, but truly reliable static analysis often inflexibly demands strict work from the programmer. There is a cost-benefit calculation, and the bar needs to be set high for a check that leads to a compile time error.

It would be more helpful if the IDE took on the role of communicating which exceptions a method may throw including which are unavoidable. Although perhaps it would not be as reliable without forced exception declarations, most exceptions would still be declared in documentation, and the reliability of an IDE warning is not so crucial.

Here 's one argument against checked exceptions from joelonsoftware. The reasoning is that I consider exceptions to be no better than "goto's", considered harmful since the s, in that they create an abrupt jump from one point of code to another.

In fact they are significantly worse than goto's:. Like provides two copies of same classes - one wrapped with RuntimeEception. Then we can compare what people would use. For now, though, many people would better go for some framework on top on java, or different language.

Like Scala, JRuby whatever. Many just believe that SUN was right. Here's an alternate point of view from a Java guy about when to use checked exceptions. He acknowledges many of the negatives others have mentioned: Effective Exceptions. Despite having read the whole page, I still can't find a single reasonable argument against checked exceptions. Most people are instead talking about poor API design, either at some Java classes or at their own classes. The only scenario where this feature may be annoying is prototiping.

This could be solved by adding some mechanism to the language for instance, some supresscheckedexceptions annotation. But for regular programming, I think checked exceptions are a good thing. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. The case against checked exceptions Ask Question.

Asked 12 years, 8 months ago. Active 5 months ago. Viewed 69k times. Every conversation I have ends with the same question going unanswered Another common argument I hear is that checked exceptions make it harder to refactor code. The question that people never reply to is this: If you throw RuntimeException subclasses instead of Exception subclasses then how do you know what you are supposed to catch? Improve this question. Robert Harvey k 44 44 gold badges silver badges bronze badges.

TofuBeer TofuBeer I don't think it's completely subjective - it's a language feature that was designed to have a specific use, rather than for everyone to decide what it's for for themselves. And it's not especially argumentative, it addresses in advance specific rebuttals which people could easily have come up with.

Come on. Viewed as a language feature, this topic has been and can be approached in an objective way. Great question. You end up in a situation where you have to put a catch around every single function call you make, because you just don't know whether it might throw something. The strongest argument I know for checked exceptions is that they weren't originally there in Java, and that when they were introduced they discovered hundreds of bugs in the JDK.

This is somewhat prior to Java 1. I personally would not be without them, and disagree violently with Bruce Eckel and others on this. Show 21 more comments.

Active Oldest Votes. It basically boils down to: "Checked exceptions are bad because programmers just abuse them by always catching them and dismissing them which leads to problems being hidden and ignored that would otherwise be presented to the user".

So, what about checked exceptions? Well here's one of the Java APIs you can use for opening a file. No really, deal with it! The API programmer is saying this to you: "You may use this constructor to create a new FileInputStream but you a must pass in the file name as a String b must accept the possibility that the file might not be found at runtime" And that's the whole point as far as I'm concerned.

I have the table model somewhere with an API including this method: public RowData getRowData int row Now as an API programmer I know there will be cases where some client passes in a negative value for the row or a row value outside of the table. But I'm not happy throwing the baby out with the bathwater here, so allow me to extract some rules here to distinguish good checked exceptions from bad: Out of client's control or Closed vs Open: Checked exceptions should only be used where the error case is out of control of both the API and the client programmer.

Ubiquity: Checked exceptions should not be used on an API call that is made frequently by the client. In particular, I'm going to be writing a lot of code like if model. Informing the User: Checked exceptions should be used in cases where you can imagine a useful error message being presented to the end user. Since you can predict that something outside of your client-API system might cause the file to not be there, you can reasonably tell the user about it: "Error: could not find the file 'goodluckfindingthisfile'" Since your illegal row number was caused by an internal bug and through no fault of the user, there's really no useful information you can give them.

If your app doesn't let runtime exceptions fall through to the console it will probably end up giving them some ugly message like: "Internal error occured: IllegalArgumentException in Sorry, didn't mean to make this so long and waffly.

Let me finish with two suggestions: A: API programmers: use checked exceptions sparingly to preserve their usefulness. Here's the constructor: public RuntimeException Throwable cause Then get in the habit of whenever you have to handle a checked exception and you're feeling lazy or you think the API programmer was overzealous in using the checked exception in the first place , don't just swallow the exception, wrap it and rethrow it.

Improve this answer. Rhubarb Rhubarb Comments are not for extended discussion; this conversation has been moved to chat. Add a comment. In your code example, it would be best to chain the exceptions so that the original cause can be found when reading the logs: throw CanNeverHappenException e ; — Esko Luontola. And that IMO this does indeed lead to confusion and poor design.

Agree that the standard libraries misuse of checked exceptions definitely added to the confusion and bad catching behavior. And, often it's just from poor documentation, e. Well, I was disconnecting! Am I'm leaking a handle or other resource? Do I need to retry? Without knowing why it happened, I can't derive the action I should take and so I have to guess whether I should just swallow it, retry, or bail.

Interesting way of looking at checked exceptions. I think conceptually the idea of exceptions as an alternative return value makes sense, but I'd take it even further. It's an alternative return mechanism. Exceptions can pass the same value through multiple entries in the function call stack , silently bypassing swaths of code in the process. This is not something the normal return mechanism can do, and it is the reason that exceptions allow us to achieve decoupling.

Bottom line, exceptions are flow control , contrary to the platitude. They are a more limited, more manageable because of greater guarantees about state GOTO. Show 6 more comments. Ok, i guess that was three reasons. But if an exception is properly catched, you can inform the user, do other tasks log? I agree that some API parts could have been designed better. I think IDEs such as Eclipse have a lot to blame for the number of times you've seen the empty catch block.

Really, they should rethrow by default. Both of your examples are arts of work from bad programmers. You should be attacking the bad programmers and not checked exceptions themselves. It's like me attacking insulin for not helping with my diabetes when I use it as salad dressing. YasmaniLlanes You cannot always do these things. Sometimes you have an interface to adhere to. And this is especially true when you design good maintainable APIs because you can't just start throwing side-effects all over the place.

Both that, and the complexity it will introduce, will bite you severely on a large scale. Show 14 more comments. Except not always. Suppose that Widget has a method for saving it out to a stream: public void writeTo OutputStream out throws IOException; Declaring this method to accept a plain OutputStream is the right thing to do, so it can be used polymorphically with all kinds of outputs: files, databases, the network, and so on. Boann Boann For your size method with the WidgetList, I would cache the size in a variable and set it in the constructor.

The constructor is free to throw an exception. This won't work if the file changes while using the WidgetList though, which would probably be bad if it did. So either it never should have been thrown bad design or you should really handle it. The same is true of the bad implementation of a pre The proper idiom would have been a directive that would catch any specified exceptions thrown by nested subroutine calls and rethrow them wrapped in a RuntimeException.

Note that a routine could simultaneously be declared as throws IOException and yet also specify that any IOException thrown from a nested call should be considered unexpected and wrapped. I'm a professional C developer with some Java experience who stumbled on this post. I'm baffled as to why anyone would support this bizarre behavior. NET if I want to catch a specific type of exception, I can catch that.

If I want to just let it get thrown up the stack, there's nothing to do. I wish Java wasn't so quirky. Concerning "sometimes I'll comment out a method call temporarily" - I learnt to use if false for this.

It avoids the throw clause problem and the warning helps me to navigate back faster. Checked exceptions have some value, but this value is negligible when compared to their cost. Nearly always they just get in the way. Show 2 more comments. I've found, time and time again, and throughout the project I mentioned, that exception handling falls into 3 categories: Catch and handle a specific exception.

This is to implement retry logic, for example. Catch and rethrow other exceptions. These are errors you can't do anything about; only a higher levels knows enough to handle it.

Catch everything and display an error message. This is usually at the very root of a dispatcher, and all it does it make sure it can communicate the error to the caller via a non-Exception mechanism popup dialogue, marshaling an RPC Error object, etc. Carl Manaster Richard Levasseur Richard Levasseur You could have made specific subclasses of AppSpecificException to allow separation while keeping the plain method signatures.

It is much, much better to have the name of the file not found in the stack trace, than hidden deep down in a log file. Basically your argument is "Managing exceptions is tiring so I'd rather not deal with it". As the exception bubbles up it looses meaning and context making is practically useless.

As designer of an API you should make is contractually clear as to what can be expected when things go wrong, if my program crashes because I was not informed that this or that exception can "bubbles up" then you, as designer, failed and as a result of your failure my system is not as stable as it can be. Thats not what I'm saying at all. Your last sentence actually agrees with me.

Newtopian -- exceptions can largely only be handled at the "business" or "request" level. It makes sense to fail or retry at large granularity, not for every tiny potential failure. For this reason, exception-handling best practice is summarized as "throw early, catch late". Checked exceptions make it harder to manage reliability at the correct level, and encourage vast numbers of mis-coded catch blocks.

Show 3 more comments. SNR Firstly, checked exceptions decrease the "signal-to-noise ratio" for the code. Jail Break To implement even the most basic of implementations, such as Java's List interface, checked exceptions as a tool for design by contract fall down. Conclusion Catching exceptions is different to handling them. Checked exceptions add noise to the code. Exception handling works well in C without them. Luke Quinane Luke Quinane 16k 13 13 gold badges 65 65 silver badges 87 87 bronze badges.

In the example both Java and C are just letting the exceptions propagate up without handling them Java via IllegalStateException. Also I would never throw an exception from run I consider that abusing exception handling.

Sorry but for that part of your code I just can see your side of it yet. We are getting there :- So with each new release of an API you have to comb through all your calls and look for any new exceptions that might happen?

The can easily happen with internal to a company APIs since they don't have to worry about backwards compatibility. Did you mean decrease the signal-to-noise ratio? TofuBeer Isn't being forced to update your code after the interface of an underlaying API changed a good thing? Show 5 more comments. A short taster: The throws clause, at least the way it's implemented in Java, doesn't necessarily force you to handle the exceptions, but if you don't handle them, it forces you to acknowledge precisely which exceptions might pass through.

Le Dude Le Dude 5 5 silver badges 9 9 bronze badges. I have read that, to me his argument boils down to "there are bad programmers out there". TofuBeer, not at all. The whole point is that many times you don't know what to do with the Exception that the called method throws, and the case you're really interested in isn't even mentioned. You open a file, you get an IO Exception, for instance But the top-level calling method will just want to stop processing and inform the user that there's an unknown problem.

The checked Exception didn't help at all. It was one of a million strange things that can happen. TofuBeer, I think his real argument is that there are humans out there. And that on the whole, it's not convincing that the pain incurred using checked exceptions is less than the pain incurred without them.

What matters is not what went wrong, but what state objects are in. Further, both. Show 8 more comments. Here are some quotes from that article to highlight the main points: Contingency: An expected condition demanding an alternative response from a method that can be expressed in terms of the method's intended purpose.

Contingency Is considered to be: A part of the design Is expected to happen: Regularly but rarely Who cares about it: The upstream code that invokes the method Examples: Alternative return modes Best Mapping: A checked exception Fault Is considered to be: A nasty surprise Is expected to happen: Never Who cares about it: The people who need to fix the problem Examples: Programming bugs, hardware malfunctions, configuration mistakes, missing files, unavailable servers Best Mapping: An unchecked exception.

Community Bot 1 1 1 silver badge. Esko Luontola Esko Luontola I know when to use them, I want to know why people who don't follow that advice What are programming bugs and how to distinguish them from usage bugs?

Is it a programming bug if the user passes the wrong arguments to the program? From the Java point of view it might be no programming bug but from the shell script point of view it is a programming bug.

So what are invalid arguments in args[]? Are they a Contingency or a Fault? TofuBeer -- Because the Java library designers, chose to put all kinds of unrecoverable low-level failures as checked exceptions when they clearly should have been unchecked. With regard to JDBC -- only connecting to the database, can reasonably be considered a contingency. All other SQLExceptions should have been failures and unchecked. Error handling should correctly be at the "business" or "request" level -- see the "throw early, catch late" best practice.

Checked exceptions are a barrier to that. There is a single huge flaw in your argument. MatteoMosca Error return codes tend to get ignored and that's enough to disqualify them.

Actually, anything unusual can oftentimes be only handled somewhere up in the stack and that's a use case for exceptions. Show 1 more comment. Java encourages you to do this sort of thing, so that you don't have to add every type of exception to every method signature. An empty catch block swallows the exception. We will never be informed when the exception occurs. The application will behave incorrectly and we have no clue why.

Happy debugging. Checked exceptions are extremely annoying when it comes to lambdas and streams. Since the IOException is not declared in the functional interface for the lambda java.

This try-catch-boilerplate blows up our code and makes it less readable. If you define your own exception, always use unchecked exceptions RuntimeException.

Now the client of getContent or getUsers has the freedom to handle the RepositoryException at the point where it is most appropriate. The client decides, not the compiler. He can let the exception fly up to a central point where all exceptions are handled and, for instance, provide feedback to the user.

Is there a possible recovery for the RepositoryException? Fine, then do it. You should not forget to catch the RepositoryException if you want to handle it. You should throw an exception that captures the issue that caused it. RunTimeException is broad and over reaching.

Whatever accurately describes what went wrong. This provides the ability to differentiate issues that you should handle and let the program survive versus errors that should be a "Do not pass go" scenario.

What he is doing is only slightly better than "On Error Resume Next" unless there is something missing in the info provided in the question. This practice may be even wise. There are many situations for example in web developement , where if some exception happens, you are unable to do anything because you cannot for example repair inconsistent DB from your code :- , only developer can do it.

In these situations, it is wise to wrap the thrown exception into a runtime exception a rethrow it. On the other hand , if the exception is not runtime is checked , the developer of the API indicates, that this exception is resolvable and should be repaired.

If its possible, than you should definitely do it. The other solution might be to rethrow this checked exception into the calling layer, but if you were unable to solve it, where the exception occured, you will be likely unable to solve it here also I would like to get comments on this, but I find there are times when this isn't necessarily bad practice. Or terribly bad. But maybe i am wrong. Often times an API you are using will throw an exception that you can't imagine actually being thrown in your specific usecase.

In this case, it seems perfectly fine to throw a RuntimeException with the caught exception as the cause. If this exception is thrown, it'll likely be the cause of programming error and isn't inside the bounds for correct specification.

The OnErrorResumeNext would occur when someone catches an exception and simply ignores it or just prints it out. This is terribly bad practice in almost all cases.

We may rethrow a checked exception as a runtime exception if the propagating or interface code assumes that the underlying implementation depends on external state, when it clearly does not.

This section discusses the topic of when either of the exceptions should be thrown. You can skip to the next horizontal bar if you just want to read a more detailed explanation for the conclusion. When is it appropriate to throw a runtime exception? You throw a runtime exception when it is clear that the code is incorrect, and that recovery is appropriate by modifying the code.

This will throw a division by zero runtime exception. This is appropriate because the code is defective. In order to fix the initial capacity or load factor, it is appropriate that you edit the code to ensure that the correct values are being passed in. It is not dependent on some far away server being up, on the current state of the disk, a file, or another program.

That constructor being called with invalid arguments depends on the correctness of the calling code, be it a wrong calculation that led to the invalid parameters or inappropriate flow that missed an error. When is it appropriate to throw a checked exception? You throw a checked exception when the issue is recoverable without changing the code.

Or to put it in different terms, you throw a checked exception when the error is related to state while the code is correct. Now the word "recover" may be tricky here. It could mean that you find another way to achieve the goal: For instance, if the server doesn't respond then you should try the next server.

If that sort of recovery is possible for your case then that's great, but that's not the only thing recovery means -- recovery could simply be displaying an error dialog to the user that explains what happened, or if that's a server application then it could be sending an email to the administrator, or even merely logging the error appropriately and concisely.

This is not the correct way to handle the checked exception. The mere incapacity to handle the exception in this method's scope does not mean that the app should be crashed. Instead, it is appropriate to propagate it to a higher scope like so:. Checked exceptions are a static-analysis tool, they make it clear for a programmer what could go wrong in a certain call without requiring them to learn the implementation or going through a trial and error process.

This makes it easy to ensure that no portions of the error flow will be ignored. Rethrowing a checked exception as a runtime exception is working against this labor-saving static analysis feature.

It is also worth mentioning that the calling layer has a better context of the grander scheme of things as has been demonstrated above. There could be many causes for that dataAccessCode would be called, the specific reason for the call is only visible to the caller -- thus it is able to make a better decision at the correct recovery upon failure. Now that we've got this distinction clear, we may proceed to deduce when it's ok to rethrow a checked exception as a runtime exception.

Given the above, when is it appropriate to rethrow a checked exception as a RuntimeException? When the code you are using assumes dependency on external state, but you can clearly assert that it does not depend on external state.

In this example, the code is propagating IOException because the API of Reader is designed to access external state, however we know that StringReader implementation does not access external state. At this scope, where we can certainly assert that the parts involved in the call don't access IO or any other external state, we can safely rethrow the exception as a runtime exception without astonishing colleagues who are unaware of our implementation and are possibly assuming that IO-accessing code will throw an IOException.

The reason for strictly keeping external state dependent exceptions checked is that they are non-deterministic unlike logic dependent exceptions, which will predictably be reproduced every time for a version of the code.

For example, if you try to divide by 0, you will always produce an exception. If you don't divide by 0, you will never produce an exception, and you don't have to handle that exception case, because it will never happen. In the case of accessing a file, however, succeeding once does not mean that you will succeed next time -- the user might have changed permissions, another process might have deleted or modified it.

So you always have to handle that exceptional case, or you likely have a bug. For standalone applications. When you know your application cannot handle the exception you could, instead of throwing the checked RuntimeException, throw Error, let the application crash, hope for bug-reports, and fix your application. See the answer of mrmuggles for a more in depth discussion of the pro's and con's of checked versus unchecked.

This is common practice in many frameworks.