java.lang.Object
java.text.Collator
java.text.RuleBasedCollator
public class RuleBasedCollator
The 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) :
The collation table is composed of a list of collation rules, where each rule is of one of three forms:
<modifier>
<relation> <text-argument>
<reset> <text-argument>
The definitions of the rule elements is as follows:
b c is treated as bc.'@' : 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 a-umlaut is treated as though it expanded to two characters (expressed as "a,A < b,B ... &ae;\u00e3&AE;\u00c3"). [\u00e3 and \u00c3 are, of course, the escape sequences for a-umlaut.]a < b & a < c a < c & a < 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
RuleBasedCollator automatically processes its rule table to include both pre-composed and combining-character versions of accented characters. Even if the provided rule string contains only base characters and separate combining accent characters, the pre-composed accented characters matching all canonical combinations of characters from the rule string will be entered in the table.
This allows you to use a RuleBasedCollator to compare accented strings even when the collator is set to NO_DECOMPOSITION. There are two caveats, however. First, if the strings to be collated contain combining sequences that may not be in canonical order, you should set the collator to CANONICAL_DECOMPOSITION or FULL_DECOMPOSITION to enable sorting of combining sequences. Second, if the strings contain characters with compatibility decompositions (such as full-width and half-width forms), you must use FULL_DECOMPOSITION, since the rule tables only include canonical mappings.
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 < \u00E5=a\u030A,\u00C5=A\u030A ;aa,AA< \u00E6,\u00C6< \u00F8,\u00D8"
To create a RuleBasedCollator object with specialized rules tailored to your needs, you construct the RuleBasedCollator 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" +
"< \u00E5=a\u030A,\u00C5=A\u030A" +
";aa,AA< \u00E6,\u00C6< \u00F8,\u00D8";
RuleBasedCollator myNorwegian = new RuleBasedCollator(Norwegian);
A new collation rules string can be created by concatenating rules strings. For example, the rules returned by getRules() could be concatenated to combine multiple RuleBasedCollators.
The following example demonstrates how to change the order of non-spacing accents,
// old rule
String oldRules = "=\u0301;\u0300;\u0302;\u0308" // main accents
+ ";\u0327;\u0303;\u0304;\u0305" // main accents
+ ";\u0306;\u0307;\u0309;\u030A" // main accents
+ ";\u030B;\u030C;\u030D;\u030E" // main accents
+ ";\u030F;\u0310;\u0311;\u0312" // main accents
+ "< a , A ; ae, AE ; \u00e6 , \u00c6"
+ "< b , B < c, C < e, E & C < d, D";
// change the order of accent characters
String addOn = "& \u0300 ; \u0308 ; \u0302";
RuleBasedCollator myCollator = new RuleBasedCollator(oldRules + addOn);
Collator, CollationElementIterator
public RuleBasedCollator(String rules)
throws ParseException
rules - the collation rules to build the collation table from.
ParseException - A format exception will be thrown if the build process of the rules fails. For example, build rule "a < ? < d" will cause the constructor to throw the ParseException because the '?' is not quoted.
Locale
public String getRules()
public CollationElementIterator getCollationElementIterator(String source)
CollationElementIterator
public CollationElementIterator getCollationElementIterator(CharacterIterator source)
CollationElementIterator
public int compare(String source,
String target)
compare in class Collator
source - the source string.
target - the target string.
CollationKey, Collator.getCollationKey(java.lang.String)
public CollationKey getCollationKey(String source)
getCollationKey in class Collator
source - the string to be transformed into a collation key.
CollationKey, Collator.compare(java.lang.String, java.lang.String)
public Object clone()
clone in class Collator
Cloneable
public boolean equals(Object obj)
equals in interface Comparator<Object>
equals in class Collator
obj - the table-based collation object to be compared with this.
Object.hashCode(), Hashtable
public int hashCode()
hashCode in class Collator
Object.equals(java.lang.Object), Hashtable
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