Java的equalsIgnoreCase的正确替代是什么？

Question

There are lots and lots of examples on why and when java.lang.String.equalsIgnoreCase will fail because of incorrect use of the locale.

But I did not find any examples of the correct way. Unlike java.lang.String.toUpperCase there is no version with a locale parameter. Converting both strings to upper or lower case seem to be wasteful. Especially when you are working on a application doing a lot of comparisons.

What is the correct way to make a ignore case string comparison, taking both locale and performance into consideration?

Answer 1

According to this page , you can use Collator to do case insensitive equality as follows:

//retrieve the runtime user's locale
Locale locale = new Locale(getUserLocale());

//pass the user's locale as an argument
Collator myCollator = Collator.getInstance(locale);

//set collator to Ignore case but not accents
//(default is Collator.TERTIARY, which is
//case sensitive)
myCollator.setStrength(Collator.SECONDARY);

int i = myCollator.compare(stringA,stringB);

(Copied from the above site ...)

Obviously, in other contexts you might choose the locale differently.

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For @fge - This Oracle Bug Report gives an example of the kind of thing that happens.

• http://bugs.java.com/bugdatabase/view_bug.do?bug_id=4425387

Answer 2

A possible alternative might be abusing Regex. This is quite performance-intensive with dynamically changing strings, but if you are comparing against constants it could be an alternative:

Matcher matcher = Pattern.compile("^" + myOtherString + "$",
    Pattern.CASE_INSENSITIVE | Pattern.LITERAL | Pattern.UNICODE_CASE).matcher();
if (matcher.matches(myString)) {
   // ...
}

This anchors the string you want to compare against, specifies Unicode-aware case-insensitive matching of the Literal string.