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java.lang.Object
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+----java.text.Collator
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+----java.text.RuleBasedCollator
RuleBasedCollator class is a concrete subclass of
Collator that provides a simple, data-driven, table collator.
With this class you can create a customized table-based Collator.
RuleBasedCollator maps characters to sort keys.
RuleBasedCollator has the following restrictions
for efficiency (other subclasses may be used for more complex languages) :
0xE800-0xF8FF.
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:
'@' : 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:
a < b < c
a < b & b < c
a < c & a < b
Notice that the order is important, as the subsequent item goes immediately
after the text-argument. The following are not equivalent:
a < b & a < 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 "Д"
(a-umlaut) is treated as though it expands to two characters (expressed as
"a & ae ; Д < b").
Ignorable Characters
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
The 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. Collator
also uses the Unicode canonical mapping to ensure that combining sequences
are sorted properly (for more information, see
The Unicode Standard, Version 2.0.)
Errors
The following are errors:
RuleBasedCollator throws
a ParseException.
Examples
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 < Е=a?,е=A? ;aa,AA< Ц,ц< Ы,ы"
Normally, to create a rule-based Collator object, you will use
Collator's factory method getInstance.
However, to create a rule-based Collator object with specialized
rules tailored to your needs, you construct the RuleBasedCollator
with the rules contained in a String object. For example:
String Simple = "< a < b < c < d";
RuleBasedCollator mySimple = new RuleBasedCollator(Simple);
Or:
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" +
"< Е=a?,е=A?" +
";aa,AA< Ц,ц< Ы,ы";
RuleBasedCollator myNorwegian = new RuleBasedCollator(Norwegian);
Combining Collators is as simple as concatenating strings.
Here's an example that combines two Collators from two
different locales:
// 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
your own:
// 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 ; Ц , ц"
+ "< 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 Collator, you
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);
RuleBasedCollator(String)
clone()
compare(String, String)
equals(Object)
getCollationElementIterator(String)
getCollationKey(String)
getRules()
hashCode()
RuleBasedCollator
public RuleBasedCollator(String rules) throws ParseException
getRules
public String getRules()
getCollationElementIterator
public CollationElementIterator getCollationElementIterator(String source)
compare
public int compare(String source,
String target)
getCollationKey
public CollationKey getCollationKey(String source)
clone
public Object clone()
equals
public boolean equals(Object obj)
hashCode
public int hashCode()
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