public class RuleBasedCollator extends Collator
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:
a < b < c a < b & b < c a < c & a < bNotice 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 < bEither 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.]
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 < \u00E6, \u00C6 < \u00F8, \u00D8 < \u00E5 = a\u030A, \u00C5 = A\u030A; aa, AA"
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:
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" + "< \u00E6, \u00C6" + // Latin letter ae & AE "< \u00F8, \u00D8" + // Latin letter o & O with stroke "< \u00E5 = a\u030A," + // Latin letter a with ring above " \u00C5 = A\u030A;" + // Latin letter A with ring above " aa, AA"; 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 RuleBasedCollator
s.
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
CANONICAL_DECOMPOSITION, FULL_DECOMPOSITION, IDENTICAL, NO_DECOMPOSITION, PRIMARY, SECONDARY, TERTIARY
public RuleBasedCollator(String rules) throws ParseException
RuleBasedCollator constructor. This takes the table rules and builds a collation table out of them. Please see RuleBasedCollator class description for more details on the collation rule syntax.
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()
Gets the table-based rules for the collation object.
public CollationElementIterator getCollationElementIterator(String source)
Returns a CollationElementIterator for the given String.
source
- the string to be collatedCollationElementIterator
objectCollationElementIterator
public CollationElementIterator getCollationElementIterator(CharacterIterator source)
Returns a CollationElementIterator for the given CharacterIterator.
source
- the character iterator to be collatedCollationElementIterator
objectCollationElementIterator
public int compare(String source, String target)
Compares the character data stored in two different strings based on the collation rules. Returns information about whether a string is less than, greater than or equal to another string in a language. This can be overriden in a subclass.
compare
in class Collator
source
- the source string.target
- the target string.NullPointerException
- if source
or target
is null.CollationKey
, Collator.getCollationKey(java.lang.String)
public CollationKey getCollationKey(String source)
Transforms the string into a series of characters that can be compared with CollationKey.compareTo. This overrides java.text.Collator.getCollationKey. It can be overriden in a subclass.
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()
Standard override; no change in semantics.
public boolean equals(Object obj)
Compares the equality of two collation objects.
equals
in interface Comparator<Object>
equals
in class Collator
obj
- the table-based collation object to be compared with this.Object.hashCode()
, HashMap
public int hashCode()
Generates the hash code for the table-based collation object
hashCode
in class Collator
Object.equals(java.lang.Object)
, System.identityHashCode(java.lang.Object)
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