java.text.Collator
java.text.RuleBasedCollator
is new.
java.lang.Object
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: '@' : 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:
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
Normally, to
create a
RuleBasedCollator
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:
Or:StringSimple= "< a< b< c< d"; RuleBasedCollator mySimple = newRuleBasedCollator(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.
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 = "=\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);
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 \u2212 String jaString = "& \u2212 < \u3041, \u3042 < \u3043, \u3044"; RuleBasedCollator myJapaneseCollator = new RuleBasedCollator(en_USCollator.getRules() + jaString);
| Field Summary |
|---|
| Fields inherited from class java.text. Collator |
|---|
| CANONICAL_DECOMPOSITION , FULL_DECOMPOSITION , IDENTICAL , NO_DECOMPOSITION , PRIMARY , SECONDARY , TERTIARY |
| Constructor Summary | |
|---|---|
|
RuleBasedCollator
(
String
rules) RuleBasedCollator constructor. |
|
| Method Summary | |
|---|---|
| Object |
clone
() Standard override; no change in semantics. |
| int |
compare
(
String
source,
String
target) Compares the character data stored in two different strings based on the collation rules. |
| boolean |
equals
(
Object
obj) Compares the equality of two collation objects. |
| CollationElementIterator |
getCollationElementIterator
(
CharacterIterator
source) Return a CollationElementIterator for the given String. |
| CollationElementIterator |
getCollationElementIterator
(
String
source) Return a CollationElementIterator for the given String. |
| CollationKey |
getCollationKey
(
String
source) Transforms the string into a series of characters that can be compared with CollationKey.compareTo. |
| String |
getRules
() Gets the table-based rules for the collation object. |
| int |
hashCode
() Generates the hash code for the table-based collation object |
| Methods inherited from class java.text. Collator |
|---|
| compare , equals , getAvailableLocales , getDecomposition , getInstance , getInstance , getStrength , setDecomposition , setStrength |
| Methods inherited from class java.lang. Object |
|---|
| finalize , getClass , notify , notifyAll , toString , wait , wait , wait |
| Constructor Detail |
|---|
public RuleBasedCollator(String rules)
throws ParseException
| Method Detail |
|---|
public String getRules()
public CollationElementIterator getCollationElementIterator(String source)
public CollationElementIterator getCollationElementIterator(CharacterIterator source)
public int compare(String source,
String target)
public CollationKey getCollationKey(String source)
public Object clone()
public boolean equals(Object obj)
public int hashCode()