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java.lang.Object | +----java.text.Collator | +----java.text.RuleBasedCollator
RuleBasedCollatorclass is a concrete subclass of
Collatorthat provides a simple, data-driven, table collator. With this class you can create a customized table-based
RuleBasedCollatormaps characters to sort keys.
RuleBasedCollator has the following restrictions
for efficiency (other subclasses may be used for more complex languages) :
The collation table is composed of a list of collation rules, where each rule is of three forms:
< modifier > < relation > < text-argument > < reset > < text-argument >The following demonstrates how to create your own collation rules:
b cis treated as
'@' : Indicates that accents are sorted backwards, as in French.
'&' : Indicates that the next rule follows the position to where the reset text-argument would be sorted.
This sounds more complicated than it is in practice. For example, the following are equivalent ways of expressing the same thing:
Notice that the order is important, as the subsequent item goes immediately after the text-argument. The following are not equivalent:a < b < c a < b & b < c a < c & a < b
Either the text-argument must already be present in the sequence, or some initial substring of the text-argument must be present. (e.g. "a < b & ae < e" is valid since "a" is present in the sequence before "ae" is reset). In this latter case, "ae" is not entered and treated as a single character; instead, "e" is sorted as if it were expanded to two characters: "a" followed by an "e". This difference appears in natural languages: in traditional Spanish "ch" is treated as though it contracts to a single character (expressed as "c < ch < d"), while in traditional German "ä" (a-umlaut) is treated as though it expands to two characters (expressed as "a & ae ; ä < b").a < b & a < c a < c & a < b
For ignorable characters, the first rule must start with a relation (the examples we have used above are really fragments; "a < b" really should be "< a < b"). If, however, the first relation is not "<", then all the all text-arguments up to the first "<" are ignorable. For example, ", - < a < b" makes "-" an ignorable character, as we saw earlier in the word "black-birds". In the samples for different languages, you see that most accents are ignorable.
Normalization and Accents
Collator object automatically normalizes text internally
to separate accents from base characters where possible. This is done both when
processing the rules, and when comparing two strings.
also uses the Unicode canonical mapping to ensure that combining sequences
are sorted properly (for more information, see
The Unicode Standard, Version 2.0.)
The following are errors:
Simple: "< a < b < c < d"
Norwegian: "< a,A< b,B< c,C< d,D< e,E< f,F< g,G< h,H< i,I< j,J < k,K< l,L< m,M< n,N< o,O< p,P< q,Q< r,R< s,S< t,T < u,U< v,V< w,W< x,X< y,Y< z,Z < å=a?,Å=A? ;aa,AA< æ,Æ< ø,Ø"
Normally, to create a rule-based Collator object, you will use
Collator's factory method
However, to create a rule-based Collator object with specialized
rules tailored to your needs, you construct the
with the rules contained in a
String object. For example:
Or:String Simple = "< a < b < c < d"; RuleBasedCollator mySimple = new RuleBasedCollator(Simple);
String Norwegian = "< a,A< b,B< c,C< d,D< e,E< f,F< g,G< h,H< i,I< j,J" + "< k,K< l,L< m,M< n,N< o,O< p,P< q,Q< r,R< s,S< t,T" + "< u,U< v,V< w,W< x,X< y,Y< z,Z" + "< å=a?,Å=A?" + ";aa,AA< æ,Æ< ø,Ø"; RuleBasedCollator myNorwegian = new RuleBasedCollator(Norwegian);
Collators is as simple as concatenating strings.
Here's an example that combines two
Collators from two
// Create an en_US Collator object RuleBasedCollator en_USCollator = (RuleBasedCollator) Collator.getInstance(new Locale("en", "US", "")); // Create a da_DK Collator object RuleBasedCollator da_DKCollator = (RuleBasedCollator) Collator.getInstance(new Locale("da", "DK", "")); // Combine the two // First, get the collation rules from en_USCollator String en_USRules = en_USCollator.getRules(); // Second, get the collation rules from da_DKCollator String da_DKRules = da_DKCollator.getRules(); RuleBasedCollator newCollator = new RuleBasedCollator(en_USRules + da_DKRules); // newCollator has the combined rules
Another more interesting example would be to make changes on an existing
table to create a new
Collator object. For example, add
"& C < ch, cH, Ch, CH" to the
en_USCollator object to create
// Create a new Collator object with additional rules String addRules = "& C < ch, cH, Ch, CH"; RuleBasedCollator myCollator = new RuleBasedCollator(en_USCollator + addRules); // myCollator contains the new rules
The following example demonstrates how to change the order of non-spacing accents,
// old rule String oldRules = "=?;?;?;?" // main accents + ";?;?;?;?" // main accents + ";?;?;?;?" // main accents + ";?;?;?;?" // main accents + ";?;?;?;?" // main accents + "< a , A ; ae, AE ; æ , Æ" + "< b , B < c, C < e, E & C < d, D"; // change the order of accent characters String addOn = "& ? ; ? ; ?"; RuleBasedCollator myCollator = new RuleBasedCollator(oldRules + addOn);
The last example shows how to put new primary ordering in before the
default setting. For example, in Japanese
can either sort English characters before or after Japanese characters,
// get en_US Collator rules RuleBasedCollator en_USCollator = (RuleBasedCollator)Collator.getInstance(Locale.US); // add a few Japanese character to sort before English characters // suppose the last character before the first base letter 'a' in // the English collation rule is ? String jaString = "& ? < ?, ? < ?, ?"; RuleBasedCollator myJapaneseCollator = new RuleBasedCollator(en_USCollator.getRules() + jaString);
public RuleBasedCollator(String rules) throws ParseException
public String getRules()
public CollationElementIterator getCollationElementIterator(String source)
public int compare(String source, String target)
public CollationKey getCollationKey(String source)
public Object clone()
public boolean equals(Object obj)
public int hashCode()
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