Is it good practice to catch a checked exception and throw a RuntimeException?

Question

I read some code of a colleague and found that he often catches various exceptions and then always throws a 'RuntimeException' instead. I always thought this is very bad practice. Am I wrong?

Answer 1

I do not know enough context to know whether your colleague is doing something incorrectly or not, so I am going to argue about this in a general sense.

I do not think it is always an incorrect practice to turn checked exceptions into some flavor of runtime exception. Checked exceptions are often misused and abused by developers.

It is very easy to use checked exceptions when they are not meant to be used (unrecoverable conditions, or even control flow). Especially if a checked exception is used for conditions from which the caller cannot recover, I think it is justified to turn that exception to a runtime exception with a helpful message/state. Unfortunately in many cases when one is faced with an unrecoverable condition, they tend to have an empty catch block which is one of the worst things you can do. Debugging such an issue is one of the biggest pains a developer can encounter.

So if you think that you are dealing with a recoverable condition, it should be handled accordingly and the exception should not be turned into a runtime exception. If a checked exception is used for unrecoverable conditions, turning it into a runtime exception is justified.

Answer 2

It can be GOOD. Please read this onjava.com article:

Most of the time, client code cannot do anything about SQLExceptions. Do not hesitate to convert them into unchecked exceptions. Consider the following piece of code:

public void dataAccessCode(){
  try{
      ..some code that throws SQLException
  }catch(SQLException ex){
      ex.printStacktrace();
  }
} 

This catch block just suppresses the exception and does nothing. The justification is that there is nothing my client could do about an SQLException. How about dealing with it in the following manner?

public void dataAccessCode(){
   try{
       ..some code that throws SQLException
   }catch(SQLException ex){
       throw new RuntimeException(ex);
   }
} 

This converts SQLException to RuntimeException. If SQLException occurs, the catch clause throws a new RuntimeException. The execution thread is suspended and the exception gets reported. However, I am not corrupting my business object layer with unnecessary exception handling, especially since it cannot do anything about an SQLException. If my catch needs the root exception cause, I can make use of the getCause() method available in all exception classes as of JDK1.4.

Throwing checked exceptions and not being able to recover from it is not helping.

Some people even think that checked exceptions should not be used at all. See http://www.ibm.com/developerworks/java/library/j-jtp05254/index.html

Recently, several well-regarded experts, including Bruce Eckel and Rod Johnson, have publicly stated that while they initially agreed completely with the orthodox position on checked exceptions, they've concluded that exclusive use of checked exceptions is not as good an idea as it appeared at first, and that checked exceptions have become a significant source of problems for many large projects. Eckel takes a more extreme view, suggesting that all exceptions should be unchecked; Johnson's view is more conservative, but still suggests that the orthodox preference for checked exceptions is excessive. (It's worth noting that the architects of C#, who almost certainly had plenty of experience using Java technology, chose to omit checked exceptions from the language design, making all exceptions unchecked exceptions. They did, however, leave room for an implementation of checked exceptions at a later time.)

Also from the same link:

The decision to use unchecked exceptions is a complicated one, and it's clear that there's no obvious answer. The Sun advice is to use them for nothing, the C# approach (which Eckel and others agree with) is to use them for everything. Others say, "there's a middle ground."

Answer 3

No, you are not wrong. His practice is extremely misguided. You should throw an exception that captures the issue that caused it. RunTimeException is broad and over reaching. It should be a NullPointerException, ArgumentException, etc. 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.

Answer 4

It depends.

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. Than you can catch all these exceptions in some exception handling layer, log the error and display the user some nice localized error code + message.

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...

Answer 5

TL;DR

Premise

• Runtime exceptions should be thrown when the error is irrecoverable: when the error is in the code, and does not depend on external state (thus, the recovery would be correcting the code).
• Checked exceptions should be thrown when the code is correct, but external state is not as expected: no network connectivity, file not found or is corrupt, etc.

Conclusion

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.

For instance, it is appropriate to throw a runtime exception for the following:

float nan = 1/0;

This will throw a division by zero runtime exception. This is appropriate because the code is defective.

Or for instance, here's a portion of HashMap's constructor:

public HashMap(int initialCapacity, float loadFactor) {
    if (initialCapacity < 0)
        throw new IllegalArgumentException("Illegal initial capacity: " + initialCapacity);
    if (initialCapacity > MAXIMUM_CAPACITY)
        initialCapacity = MAXIMUM_CAPACITY;
    if (loadFactor <= 0 || Float.isNaN(loadFactor))
        throw new IllegalArgumentException("Illegal load factor: " +
                loadFactor);
    // more irrelevant code...
}

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.

Let's take the example that was mentioned in mrmuggles' answer:

public void dataAccessCode(){
   try{
       ..some code that throws SQLException
   }catch(SQLException ex){
       throw new RuntimeException(ex);
   }
}

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:

public Data dataAccessCode() throws SQLException {
    // some code that communicates with the database
}

Which allows for the possibility of recovery by the caller:

public void loadDataAndShowUi() {
    try {
        Data data = dataAccessCode();
        showUiForData(data);
    } catch(SQLException e) {
        // Recover by showing an error alert dialog
        showCantLoadDataErrorDialog();
    }
}

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.

Consider the following:

StringReader sr = new StringReader("{\"test\":\"test\"}");
try {
    doesSomethingWithReader(sr); // calls #read, so propagates IOException
} catch (IOException e) {
    throw new IllegalStateException(e);
}

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.

Answer 6

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.

Assuming the RuntimeException isn't later caught and ignored, it's no where near an OnErrorResumeNext.

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.

Answer 7

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.)

Answer 8

This is common practice in many frameworks. E.g. Hibernate does exactly this. The idea is that the APIs should not be intrusive for client side and Exception are intrusive since you must explicitly write code to handle them at that place where you call the api. But that place might not be the right place to handle the exception in the first place.
Actually to be honest this is a "hot" topic and many dispute so I will not take a side but I will say that what your friend does/proposes is not un-ordinary or uncommon.

Answer 9

The whole "checked exception" thing is a bad idea.

Structured programming only allows information to be passed between functions (or, in Java parlance, methods) when they are "nearby". More precisely, information can only move across functions in two ways:

1. From a caller to a callee, via argument passing.

2. From a callee to its caller, as return values.

This is a fundamentally good thing. This is what allows you to reason about your code locally: if you need to understand or modify a part of your program, you only need to look at that part and other "nearby" ones.

However, in some circumstances, it is necessary to send information to a "distant" function, without anyone in the middle "knowing". This is precisely when exceptions have to be used. An exception is a secret message sent from a raiser (whatever part of your code might contain a throw statement) to a handler (whatever part of your code might contain a catch block that is compatible with the exception that was thrown).

Checked exceptions destroy the secrecy of the mechanism, and, with it, the very reason for its existence. If a function can afford to let its caller "know" a piece of information, just send that piece of information directly as a part of the return value.

Answer 10

In a boolean question, it is hard to answer differently after two controversial answers, but I would like to give you a perspective that even mentioned in few places, it was not stressed enough for the importance it has.

With the years I found that always someone is confused about a trivial problem they are lacking understanding of some of the fundamentals.

Layering. A software application (at least supposed to be) a pile of layers one on top of another. One important expectation for good layering is that lower layers provide functionality for potentially multiple components from the upper layer.

Let's say your app has the following layers from the bottom up NET, TCP, HTTP, REST, DATA MODEL, BUSINESS.

If your business layer would like to execute a rest call ... wait for a second. Why did I say that? Why did I not say HTTP request or TCP transaction or send network packages? Because those are irrelevant for my business layer. I am not going to handle them, I am not going to look in the details of them. I am perfectly ok if they are deep in the exceptions I get as a cause and I do not want to know that they even exist.

What is more, it is bad if I do know details, because if tomorrow I would like to change the underlining transport protocols dealing with details that are specific to the TCP protocol means that my REST abstraction did not do a good job to abstract itself from the specific implementation.

When transitioning an exception up from layer to layer it is important to revisit every aspect of it and what sense it will make for the abstraction the current layer provides. It might be to replace the exception with other, it might combine several exceptions. It might also transition them from checked to unchecked or vise versa.

Of course, is the actual places you mentioned make sense is a different story, but in general - yes, it could be a good thing to do.

Answer 11

This might depend on case to case basis. In certain scenarios it is wise to do what your friend is doing, for example when you are exposing an api for some clients and you want the client to be least aware of the implementation details, where you know that certain implementation exceptions may be specific to implementation details and not exposable to the client.

By keeping the checked exceptions out of the way, you can expose api's that would enable the client to write cleaner code as the client itself might be pre-validating the exceptional conditions.

For example Integer.parseInt(String) takes a string and returns the integer equivalent of it and throws NumberFormatException in case the string is not numeric. Now imagine a form submission with a field age is converted through this method but the client would have already ensured validation on its part, so there's no point forcing the check of exception.

Answer 12

There are really a couple of questions here

1. Should you transform checked exceptions into unchecked ones?

The general rule of thumb is that exceptions that the caller is expected to catch and recover from should be checked. Other exceptions (ones where the only reasonable outcome is to abort the whole operation or where you consider them unlikely enough that worrying about handling them specifically is not worth it) should be unchecked.

Sometimes your judgement on whether an exception deserves catching and recovery is different from that of the API you are working with. Sometimes context matters, an exception that is worth handling in one situation may not be worth handling in another. Sometimes your hand is forced by existing interfaces. So yes there are legitimate reasons to turn a checked exception into an unchecked exception (or to a different type of checked exception)

2. If you are going to turn an unchecked exception into a checked exception how should you do it.

Firstly and most importantly make sure you use the exception chaining facility. That way the information from the original exception is not lost and can be used for debugging.

Secondly you have to decide what exception type to use. Using a plain runtimeexception makes it harder for the caller to determine what went wrong but if the caller is trying to determine what went wrong that may be an indication that you should not have changed the exception to make it unchecked.

Answer 13

In my opinion,

In the framework level, we should be catch runtime exceptions to reduce more block of try catch to the invoker in the same place.

In the application level, we rarely capture runtime exceptions and i think this practice was bad.