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| Summary: | Incorrect "Comparing string using ==" hint when using constants | ||
|---|---|---|---|
| Product: | java | Reporter: | dusty <dusty> |
| Component: | Hints | Assignee: | Svata Dedic <sdedic> |
| Status: | NEW --- | ||
| Severity: | normal | ||
| Priority: | P3 | ||
| Version: | 7.3.1 | ||
| Hardware: | PC | ||
| OS: | Linux | ||
| Issue Type: | ENHANCEMENT | Exception Reporter: | |
Comparison using == can be dangerous even in your case; each String compile time constant is implicitly interned. As a result, if there's a piece of code, which happens to call x = v.intern() on String v containing "dummy", STR1 and x will receive the same reference and the comparison in your example might evaluate to true inappropriately.
In case you *want* to have String constant and compare by reference, use explicit new String("dummy") to work around the implicit intern.
This enhancement would probably require a NB specific source-only annotation on the declared element; other possibility would be to @SuppressWarnings() for the unwanted hint code - should be one of the options offered in hints.
Thanks for the insight. I don't know much about string interning: am I right to say that anyway, if the content of the string is different, it's not possible to have v == s? In understand that using two different constants with the same value is certainly a good way to look for problems :) The hint could look out for @SuppressWarnings on the constant. Placing specific @SuppressWarning on a constant would also declare that the programmer intents to work with the exact instance rather than with value. |
Hello, if I have a piece of code similar to this one: public final static String STR1="dummy"; ... String s = STR1; if (s == STR1) { ... } in the "if" line the editor gives me the hint reported on the subject, but in this special case the comparison is correct (at least, I think so). I understand it's a bit tricky to deduce that when a String is only assigned by constants the comparison can be made with == and !=, but it's a bit annoying to have warnings in the code when the there is no problem, so I report it as an enhancement.