What is a suppressed exception?

java exception exception-handling try-with-resources
Raedwald picture Raedwald · Oct 21, 2011 · Viewed 59k times · Source

A comment (by user soc) on an answer to a question about tail call optimisation mentioned that Java 7 has a new feature called "suppressed exceptions", because of "the addition of ARM" (support for ARM CPUs?).

What is a "suppressed exception" in this context? In other contexts a "suppressed exception" would be an exception that was caught and then ignored (rarely a good idea); this is clearly something different.

Answer

John B picture John B · Oct 21, 2011

To clarify the quote in Jon's answer, only one exception can be thrown by a method (per execution) but it is possible, in the case of a try-with-resources, for multiple exceptions to be thrown. For instance one might be thrown in the block and another might be thrown from the implicit finally provided by the try-with-resources.

The compiler has to determine which of these to "really" throw. It chooses to throw the exception raised in the explicit code (the code in the try block) rather than the one thrown by the implicit code (the finally block). Therefore the exception(s) thrown in the implicit block are suppressed (ignored). This only occurs in the case of multiple exceptions.

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