How can I tell Eclipse to warn me when I compare Strings with == instead of .equals()

+1 A:

I dont think you can.

Using == is a valid java language feature. There would be circumstances where you would want to do this exact thing. Then what?

Probably, one fine day some programmer would want the IDE to warn him when he writes i = 10 (instead of i == 10)

Fortunately, this is where the human takes over the machine and we all have our jobs :)

Sadly, there are so many buggy systems :(

I am sure, over time you will get in the habit of using equals() for String

Mihir Mathuria 2010-02-06 06:44:30

The only good reason I've ever seen for using == *with Strings* is to demonstrate that == and equals can potentially do different things. You're right about the habit though. I am pretty much in the habit, but I slip up occasionally. It was actually a copy-and-paste error that prompted me to ask this question, so maybe I should just be more careful with copy and paste!

MatrixFrog 2010-02-06 06:53:50

"Probably, one fine day some programmer would want the IDE to warn him when he writes i = 10 (instead of i == 10)". Um, Eclipse already does that. It's under "Potential programming problems" and it's called "possible accidental boolean assignment". I don't see why you seem think that's a bad thing.

MatrixFrog 2010-02-06 06:58:38

Don't forget `String.intern()`. Interned strings can be equivalently compared by reference or value.

finnw 2010-02-06 07:03:02

IntelliJ does the very thing he is asking for with its inspections. So it is certainly possible. It does the equivalent of option 1 the asker gave (flags it in the code as a warning).

kenj0418 2010-02-06 07:10:38

+6 A:

Eclipse can never tell you that. Findbugs or PMD probably can.

EDIT : I say

Eclipse can never tell you that.

because there nothing wrong with code a == b as java code. If you want some extra help, this is where other plugins come to help.

Edit: According to Pascal Thivent, Findbugs can't do this, but it looks like PMD can. I'm leaving the link to Findbugs, though, since it's probably a useful link for people who come across this question.

fastcodejava 2010-02-06 06:45:33

It looks like those are both plugins for Eclipse, so in fact Eclipse *can* tell me. I'd prefer not to download anything but that is an option.

MatrixFrog 2010-02-06 06:55:23

Saying that "Eclipse can never tell you that" is pretty meaningless. Neither Eclipse nor any plugin can **guarantee** that `a == b` is incorrect. It is a floating boundary between what the Eclipse compiler warns about and what external plugins can warn about.

JesperE 2010-02-06 09:35:37

I'm not sure whether Findbugs tell this kind of error, but it shows a lot of similar ones (I seldom compare strings, and then I may remember to use .equals() or .contentEquals()

Zoltán Ujhelyi 2010-02-06 12:43:50

"Probably can" is not really an answer (and Findbugs doesn't detect this).

Pascal Thivent 2010-02-06 14:12:58

-1 for the previously given reason BTW (forgot to mention that I downvoted)

Pascal Thivent 2010-02-06 14:32:45

PMD does it: http://pmd.sourceforge.net/rules/index.html#String_and_StringBuffer_Rules (UseEqualsToCompareStrings rule)

MatrixFrog 2010-02-07 08:43:44

+6 A:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=39095

lbreisacher 2010-02-06 08:37:26

+1, good find!!

fastcodejava 2010-02-06 09:08:56

A:

This is correct question however Eclipse can warn you when you have variable, you are not using probably - "Local variable is never read" and this is also 'valid Java language feature' to have such variables.

Betlista 2010-07-06 15:07:05

I think you meant this as a comment, not a new answer. But yes, exactly. It's VALID to do that, but it's also sensible for Eclipse to warn you, since it PROBABLY indicates a mistake. Same with using "==" for Strings.

MatrixFrog 2010-07-06 16:50:05

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How can I tell Eclipse to warn me when I compare Strings with == instead of .equals()

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