public class RuleBasedCollator extends Collator
RuleBasedCollator has the following restrictions for efficiency
(other subclasses may be used for more complex languages):
RuleBasedCollator, the default Unicode Collation Algorithm (UCA) rule-based table is automatically searched as a backup.
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 rule elements are defined as follows:
b cis treated as
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. For example
"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 if it contracts to a
single character (expressed as
"c < ch < d"), while in traditional
German a-umlaut is treated as if it expands to two characters (expressed as
"a,A < b,B ... & ae;� & AE;�", where � and �
are the escape sequences for a-umlaut).
For ignorable characters, the first rule must start with a relation (the
examples we have used above are really fragments;
"a < b" really
"< a < b"). If, however, the first relation is not
"<", then all text-arguments up to the first
ignorable. For example,
", - < a < b" makes
"-" an ignorable
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. However, if the strings to be collated contain combining sequences that may not be in canonical order, you should set the collator to CANONICAL_DECOMPOSITION to enable sorting of combining sequences. For more information, see The Unicode Standard, Version 3.0.
The following rules are not valid:
"a < b-c < d".
"a < , b".
"a < b & e < f".
If you produce one of these errors,
RuleBasedCollator throws a
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
RuleBasedCollator with the rules contained in a
String object. For example:
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" + "< �=a?,�=a?" + ";aa,aa< �,�< �,�"; rulebasedcollator mynorwegian = new rulebasedcollator(norwegian);
Collators is as simple as concatenating strings. Here is
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 collators // 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
The next example shows to make changes on an existing table to create a new
Collator object. For example, add
"& C < ch, cH, Ch, CH" to
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 = "= � ; � ; �" + "< a , a ; ae, ae ; � , �" + "< 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 the 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);
|Modifier and Type||Method and Description|
Returns a new collator with the same collation rules, decomposition mode and strength value as this collator.
Compares the specified object with this
Returns the collation rules of this collator.
Returns an integer hash code for this object.
compare, equals, getAvailableLocales, getDecomposition, getInstance, getInstance, getStrength, setDecomposition, setStrength
public CollationElementIterator getCollationElementIterator(CharacterIterator source)
CollationElementIteratorfor the given
CharacterIterator. The source iterator's integrity will be preserved since a new copy will be created for use.
source- the source character iterator.
public CollationElementIterator getCollationElementIterator(String source)
CollationElementIteratorfor the given string.
source- the source string.
public String getRules()
rulescan be fed into the
Note that the
rules are actually interpreted as a delta to the
standard Unicode Collation Algorithm (UCA). Hence, an empty
string results in the default UCA rules being applied. This differs
slightly from other implementations which work with full
specifications and may result in different behavior.
public Object clone()
sourcetext to the
targettext according to the collation rules, strength and decomposition mode for this
RuleBasedCollator. See the
Collatorclass description for an example of use.
General recommendation: If comparisons are to be done with the same strings
multiple times, it is more efficient to generate
objects for the strings and use
CollationKey.compareTo(CollationKey) for the comparisons. If each
string is compared to only once, using
RuleBasedCollator.compare(String, String) has better performance.
public CollationKey getCollationKey(String source)
CollationKeyfor the given source text.
public int hashCode()
truemust return the same hash code value. This means that subclasses of
Objectusually override both methods or neither method.
Note that hash values must not change over time unless information used in equals comparisons also changes.
See Writing a correct
if you intend implementing your own
public boolean equals(Object obj)
RuleBasedCollatorand indicates if they are equal. In order to be equal,
objectmust be an instance of
Collatorwith the same collation rules and the same attributes.