StackTraceElement question (original) (raw)

Krystal Mok rednaxelafx at gmail.com
Mon Oct 8 14:35:09 UTC 2012

On Mon, Oct 8, 2012 at 10:25 PM, Christos Zoulas <christos at zoulas.com>wrote:

On Oct 8, 11:07pm, david.holmes at oracle.com (David Holmes) wrote: -- Subject: Re: StackTraceElement question

| > There is also the problem of having a class hierarchy like: | > | > class A extends class I | > class B extends class I | > | > and then trying to figure out if it is A or B when you just have I from | > that StackTraceElement. | | Can't say I have ever studied stacktraces in depth but I would expect to | see A or B not I as the name. I was expecting the same, but this is not the case: $ cat StackTrace.java class I { public void run() throws Exception { throw new Exception(); } } class A extends I { } public class StackTrace { public static void main(String[] args) { try { A a = new A(); a.run(); } catch (Exception e) { StackTraceElement[] ste = e.getStackTrace(); for (int i = 0; i < ste.length; i++) System.out.println(ste[i].getClassName()); } } } $ javac Stacktrace.java $ java -cp . StackTrace I StackTrace Printing "I" here is expected. After all, that's the class where you're getting run()'s implementation from. It's not designed to tell people the actual type of the receiver of a certain method invocation. And that's what you're really after, right?

| The loader issue is real, you'd have to know where to locate the class. | But another reason to not store the Class reference is that it may | prevent the class from being unloaded. For every use-case there's a | counter-use-case.

Yes, the class loader issue is real. I am not sure about the Class reference preventing the class to be unloaded; after all, the StackTraceElements are typically transient (when the exception goes out of context, they can be GC'ed); if not, then the reference can be held until the StackTraceElement is not reachable. I don't think that keeping the reference is such a big issue to even consider making this Weak. I am really worried about the security implications. As far as serialization goes, it could be made transient for compatibility. Anyway, I would be more than happy the StackTraceElement contained the outermost enclosing class instead of the immediately enclosing one. Returning the Class<?> instance is still the most versatile, but the one that needs most consideration because of its implications. christos christos

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