Java - If I return in a catch block, will the finally block be executed?

Question

This is what I'm trying to do:

try {

    //code
} catch (Exception e) {

    return false;
} finally {

    //close resources
}

Will this work? Is it bad practice? Would it be better doing this:

boolean inserted = true;

try {

    //code
} catch (Exception e) {

    inserted = false;
} finally {

    //close resources
}

return inserted;

dup alert! did you try searching? this has been asked several times over... — devnull, Jul 31 '13 at 20:30
@devnull I researched but I was not sure if it was a good thing to do. Some topics said it was OK, while other people said it wasn't very good. — Comic Sans MS Lover, Jul 31 '13 at 20:32

score 24 · Accepted Answer · answered Jul 31 '13 at 20:22

24

Yes, it will. The only things that can prevent a finally block to execute (AFAIR) are System.exit(), and an infinite loop (and a JVM crash, of course).

answered Jul 31 '13 at 20:22

JB Nizet

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... and a power outage :) (blast, you ruined it with adding the JVM crash) – ppeterka Jul 31 '13 at 20:23
But is my first example a bad practice? – Comic Sans MS Lover Jul 31 '13 at 20:24
2

The interesting bit, overlooked by many, is that `Thread#stop` will *not* prevent the `finally` from executing. – Marko Topolnik Jul 31 '13 at 20:24
@Thecoolguyacrossthestreet: No, it's not. It's completely fine. – JB Nizet Jul 31 '13 at 20:25
1

@Thecoolguyacrossthestreet I would say the first is the simplest and what I would do. – Peter Lawrey Jul 31 '13 at 20:34
1

@Thecoolguyacrossthestreet It would be a bad practice, if you had a return statement also in finally block because your catch block's return statement would be useless in that case. – Sajal Dutta Jul 31 '13 at 20:43
@SajalDutta I see... thanks. In this case I'll the first example. I'll be sure to remember not to return anything at the finally block. – Comic Sans MS Lover Jul 31 '13 at 20:47
@Thecoolguyacrossthestreet You got it! – Sajal Dutta Jul 31 '13 at 20:48
Just to add, if the main thread exits, finally block of daemon threads are also not executed. – Dhrubajyoti Gogoi Jul 31 '13 at 21:49

Marko Topolnik · Answer 2 · 2013-07-31T20:28:03.857

7

The finally block is executed always, unconditionally, as the last thing the try-catch-finally block does. Even if you execute Thread#stop against it, the finally block will still execute, just as if a regular exception ocurred.

Not just that, if you return from finally, that return value will trample over the return from either try or catch.

BTW Your first example is not just fine, but preferred. In the second example the reader must chase around the assignments to the variable, which is a tedious job and lets bugs slip through very easily.

edited Jul 31 '13 at 20:28

answered Jul 31 '13 at 20:22

Marko Topolnik

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im not agreed with `..btw ` part ,i think is better to have only one return statement but that brings me to find about that here (where did the notion of one return only come from)[http://programmers.stackexchange.com/questions/118703/where-did-the-notion-of-one-return-only-come-from] – nachokk Jul 31 '13 at 21:02
1

That's a nice writeup! (the first answer) – Marko Topolnik Aug 01 '13 at 06:32

Eng.Fouad · Answer 3 · 2013-07-31T20:25:54.960

4

Both are approximately the same. However, be careful with the following case:

int i = 0;

try
{
    //code
}
catch(Exception e)
{
    return i;
}
finally
{
    i = 1;
}

0 is what will be returned.

edited Jul 31 '13 at 20:25

answered Jul 31 '13 at 20:24

Eng.Fouad

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Then I think my example is not a good practice, right? – Comic Sans MS Lover Jul 31 '13 at 20:25
@Thecoolguyacrossthestreet The best practice is to use clean code whenever possible. – Eng.Fouad Jul 31 '13 at 20:33

score 0 · Answer 4 · answered Jul 31 '13 at 20:44

0

I just wanted to add that it's described in the specs:

If the catch block completes abruptly for reason R, then the finally block is executed.

where of course

It can be seen, then, that a return statement always completes abruptly.

answered Jul 31 '13 at 20:44

Petr

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Java - If I return in a catch block, will the finally block be executed?

4 Answers4