Unexpected exception handling during compilation

Question

I encountered the following method, which to my surprise compiled just fine:

private String getControlMessageBlocking() throws ProtocolException,
        InterruptedException, IOException {
    try {
        // <Code that may throw any of the three listed exceptions>
        return controlMessage;
    } catch (Exception e) {
        throw e;
    }

}

Why isn't it necessary for the Exception to be caught?

The fact that any type of exception might be thrown by the catch block. — Pieter Bos, Feb 20 '14 at 12:25
What code is there before the `return` statement in the `try` block, and what exceptions can this code code throw? — fge, Feb 20 '14 at 12:26
I actually think this is a good question - only 3 explicit exceptions are allowed to be thrown, but the code here is potentially throwing a different (unlisted) type. Nandkumar's answer for why this behavior is allowed is correct. — Craig Otis, Feb 20 '14 at 12:26
Is this really valid? I get an exception because of `throw e` because the method does not `throws Exception`. — Arnaud Denoyelle, Feb 20 '14 at 12:27
@ArnaudDenoyelle Which JDK version are you using? This is only allowed in JDK 7 and higher. — Craig Otis, Feb 20 '14 at 12:28
@CraigOtis Actually no, I was using Java 6 without knowing it. I learned something new today. Thank you. — Arnaud Denoyelle, Feb 20 '14 at 12:30
Related: [Rethrowing an Exception: Why does the method compile without a throws clause?](http://stackoverflow.com/questions/19913834/rethrowing-an-exception-why-does-the-method-compile-without-a-throws-clause). — rgettman, Feb 20 '14 at 16:58

score 17 · Accepted Answer · answered Feb 20 '14 at 12:25

17

It is the feature added in Java 7. Have a look at Rethrowing Exceptions with More Inclusive Type Checking

answered Feb 20 '14 at 12:25

Nandkumar Tekale

15,514
7
56
85

i think that was possbile before java 7 – Philipp Sander Feb 20 '14 at 12:27
1

From the link, "The Java SE 7 compiler performs more precise analysis of rethrown exceptions than earlier releases of Java SE" – Brian Agnew Feb 20 '14 at 12:28
@PhilippSander : oh really, then you should try it in earlier versions – Nandkumar Tekale Feb 20 '14 at 12:28
3

@Tobold - I think it answers it pretty well – Brian Agnew Feb 20 '14 at 12:29
This looks like the answer, however OP didn't include the code before the `return` in the `try` block. If said code can throw these three exceptions, then yes it is valid. – fge Feb 20 '14 at 12:30

Unexpected exception handling during compilation

1 Answers1