Overhead associated with Exception vs Throwable in Java

27
votes

I know 

throw new Exception();

has a pretty large overhead, since it creates a full stackTrace, etc.
Does

throw new Throwable();

present the same problem? Is this behaviour inherited, or does throwing a Throwable has a smaller (o no) overhead?

EDIT
From an analyst point of view, a user inserting wrong password is an exception to the normal execution order of a program. So if I have:

public Session newSession() {  
  validate_user_and_password();   
}

throwing a UserNotValidException would sound correct from an analysts point of view.
Returning null or 0 just sounds incorrect if your code has pretty good abstraction. I just wanted to know if I could actually implement this in code, or if I'd have to just leave it to theory.

There's a good difference between programming-point-of-view exception and analyst-point-of-view exception.

Note: I've given a really simple and silly example, this is not quite my case.
Note 2: I know returning null would be the ordinary thing, but I'm required to have properly abstracted and OO code, and, personally, I see no harm in this.

8
javaexceptionthrowable
Why this concern? What's the functional requirement? – BalusC
You shouldn't be using exceptions in the regular case anyway - they should only be used in exception al circumstances. – Anon.
@anon they should be used for "exceptional code paths" which may or may not be as exceptional as one might think. For example, if you avoid filling in the stack trace, it is most performant to use them to signal the end of a stream rather than checking for the end after each read. (This does not apply for looping over arrays though, where the full length is known to the VM.) – akuhn
Think he meant "analyst" as in "business analyst". – BalusC
"annalist" means "historian". – Josh Lee

8 Answers

49
votes

Throwable also creates a stacktrace when it's created. From the java docs for Throwable:

throwable contains a snapshot of the execution stack of its thread at the time it was created.

So in terms of overhead with regards to creating a stacktrace, there should be no difference between Exception and Throwable.

If you are using exceptions for "exceptional events" (as you should be), then you shouldn't be too concerned with the overhead of a stacktrace. An exceptional event occurs rarely in running code. So Exceptions shouldn't impact the performance of normal code in any significant way.

37
votes

Nope, you need your own subclass to avoid that effect.

Exception ex = new Exception() {
    @Override public Throwable fillInStackTrace() {
        return this; // and do nothing else
    }
};

This creates an instance of exception that will not fill the stack trace (the creation of exceptions delegates to fillInStackTrace to actually fill the stack trace) and is thus cheap to create.

3
votes

With JIT compilation, it is actually not still the case that there is a lot of overheard to throwing an Exception in Java. But throwing a Throwable is not much different, since you will get a stack trace there as well.

If you are interested, there is a very interesting paper called "Efficient Java exception handling in just-in-time compilation" (link). Not a light read, but quite informative.

1
votes

You should never be throwing or catching Throwable. The scope of the exception is far too great.

As stated previously, exceptions should be used only where needed, ie: in exceptional circumstances and should be specific to the situation that spawned them. That aside, catching a Throwable implies a host of exceptions, such as OutOfMemoryException. An error of this magnitude can not be recovered from (easily) and should not be handled by the developer.

1
votes

Throwable is parent class of Exception. so Exception class is inherited from Throwable.

1
votes

Throwable vs. Exception

Java Exception

As @mangoDrunk said:"Throwable is the superclass of exception and error."

1
votes

You can look at the source code of the two classes to see that Exception doesn't do anything beyond expose the same constructors as Throwable. All of the meat, and hence overhead, lives in Throwable.

Even if Exception did introduce some additional overhead it would be a clear over-optimization to use Throwable instead. Use the right tool for the job, don't co-opt the wrong tool just because it's lighter.

0
votes

java.lang.Exception extends java.lang.Throwable, so it's the same overhead. From the Javadoc:

The Throwable class is the superclass of all errors and exceptions in the Java language. Only objects that are instances of this class (or one of its subclasses) are thrown by the Java Virtual Machine or can be thrown by the Java throw statement. Similarly, only this class or one of its subclasses can be the argument type in a catch clause.

Instances of two subclasses, Error and Exception, are conventionally used to indicate that exceptional situations have occurred. Typically, these instances are freshly created in the context of the exceptional situation so as to include relevant information (such as stack trace data).