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POWhere can I find a specific set of collation rules for equality comparison of strings?
 

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  1. POWhere can I find a specific set of collation rules for equality comparison of strings?
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    <p>We all know that using String's equals() method for equality comparison will fail miserably. Instead, one should use <a href="http://docs.oracle.com/javase/7/docs/api/java/text/Collator.html">Collator</a>, like this:</p> <pre><code>// we need to detect User Interface locale somehow Locale uiLocale = Locale.forLanguageTag("da-DK"); // Setting up collator object Collator collator = Collator.getInstance(uiLocale); collator.setStrength(Collator.SECONDARY); collator.setDecomposition(Collator.CANONICAL_DECOMPOSITION); // strings for equality testing String test1 = "USA lover Grækenland støtte"; String test2 = "USA lover graekenland støtte"; boolean result = collator.equals(test1, test2); </code></pre> <p>Now, this code works, that is result is true <strong><em>unless</em></strong> uiLocale is set to Danish. In such case it will yield false. I certainly understand <strong><em>why</em></strong> this happened: this is just because the method equals is implemented like this:</p> <pre><code>return compare(s1, s2) == Collator.Equal; </code></pre> <p>This method calls the one that is used for sorting and check if strings are the same. They are not, because Danish specific collation rules requires that <strong>æ</strong> to be sorted after (if I understand the result of compare method correctly) <strong>ae</strong>. However, these strings are <strong>really</strong> the same, with this strength both case differences and such compatibility characters (that's what its called) should be treated as equal.</p> <p>To fix this, one would use <a href="http://docs.oracle.com/javase/7/docs/api/java/text/RuleBasedCollator.html">RuleBasedCollator</a> with specific set of rules that will work for the equality case.<br> Finally the question is: does anyone know where I can get such specific rules (not only for Danish, but for other languages as well), so that compatibility characters, ligatures, etc. be treated as equal (<a href="http://cldr.unicode.org/index">CLDR</a> <a href="http://unicode.org/repos/cldr-tmp/trunk/diff/summary/da.html">chart</a> does not seem to contain such or I failed searching for it)?</p> <p>Or maybe I want to do something stupid here, and I should really use simply <a href="http://unicode.org/reports/tr10/">UCA</a> for equality comparison (any code sample, please)?</p>
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    1. USPaweł Dyda
    1. USPaweł Dyda
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      1. POWhere can I find a specific set of collation rules for equality comparison of strings?
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    2. VO
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      1. POWhere can I find a specific set of collation rules for equality comparison of strings?
      1. USMatt Fenwick
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      1. POWhere can I find a specific set of collation rules for equality comparison of strings?
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    1. COStrings equals() does exactly what its supposed to be doing and comparing words with equivalent spelling in certain languages is not part of that, so i find saying it fails miserably is misleading.
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      1. POWhere can I find a specific set of collation rules for equality comparison of strings?
      1. USStefan
    2. CO@Stefan: The problem is it is not. For example for strings containing accented characters or umlauts (à or ä) it will return **false** if one of the strings would use canonical decomposition. The spelling might be the same, doesn't matter. Even worse results will give you equalsIgnoreCase() - case variants like sharp s or final sigma won't be recognized. That's just because these methods use binary comparison which is not suitable for international strings.
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      1. POWhere can I find a specific set of collation rules for equality comparison of strings?
      1. USPaweł Dyda
    3. COthe keyword is canonical decomposition. This is a (natural) language feature and has nothing to do with String represantation, actually in most cases you want them to be treated differently as a String. I agree with you on equalsIgnoreCase that one is bad because it blurrs the line between a String that is just a container for Characters and Words in a Language/Locale.
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      1. POWhere can I find a specific set of collation rules for equality comparison of strings?
      1. USStefan
 

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