Question

Can I create a Exception like

A a = new A (new B ( new A ) );

where A and B are two different type of Exception.

I know Java can do it but is it right to do that ?

Edit : I am writing an retry on type of Exception so I am checking the getCause of the Exception. I am breaking when getCause is null or getCause equal itself , Should I also break when getCause equals any Exception seen so far

Answer 1

AException a = new AException (new BException ( new AException ) );

This is legal.

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You can also initialize the cause directly using the initCause(Throwable) method.

If you try to make exception its own cause; e.g.

 AException a = new AException();
 a.initCause(a);

you will get an IllegalArgumentException("Self-causation not permitted"). (Thanks to Joachim Sauer for pointing that out.)

While, the JVM will not stop you creating an indirect cycle, it is a really bad idea nonetheless.

• It is an abuse of the Throwable API. It makes no logical sense for an exceptional event to have caused itself, directly or indirectly.

• There is likely be code out there that assumes that the “cause” chain of an exception doesn’t have any cycles. Such code is likely to fail in a nasty way if it ever encounters a pathological exception with a cause cycle.

Note that current generation (Java 7) printStackTrace() detects and deals with a “cause” cycles, but earlier generations did not:

• http://srl.cs.berkeley.edu/~mhn/ftp/java/lang/Throwable.java.html
• http://javasourcecode.org/html/open-source/jdk/jdk-6u23/java.lang/Throwable.java.html