Cloneable
, Comparator<Object>
RuleBasedCollator
public abstract class Collator extends Object implements Comparator<Object>, Cloneable
Collator
class performs locale-sensitive String
comparison. You use this class to build searching and sorting routines for natural language text. Collator
is an abstract base class. Subclasses implement specific collation strategies. One subclass, RuleBasedCollator
, is currently provided with the Java Platform and is applicable to a wide set of languages. Other subclasses may be created to handle more specialized needs.
Like other locale-sensitive classes, you can use the static factory method, getInstance
, to obtain the appropriate Collator
object for a given locale. You will only need to look at the subclasses of Collator
if you need to understand the details of a particular collation strategy or if you need to modify that strategy.
The following example shows how to compare two strings using the Collator
for the default locale.
// Compare two strings in the default locale
Collator myCollator = Collator.getInstance();
if (myCollator.compare("abc", "ABC") < 0) {
System.out.println("abc is less than ABC");
} else {
System.out.println("abc is greater than or equal to ABC");
}
You can set a Collator
's strength property to determine the level of difference considered significant in comparisons. Four strengths are provided: PRIMARY
, SECONDARY
, TERTIARY
, and IDENTICAL
. The exact assignment of strengths to language features is locale dependent. For example, in Czech, "e" and "f" are considered primary differences, while "e" and "ě" are secondary differences, "e" and "E" are tertiary differences and "e" and "e" are identical. The following shows how both case and accents could be ignored for US English.
// Get the Collator for US English and set its strength to PRIMARY
Collator usCollator = Collator.getInstance(Locale.US);
usCollator.setStrength(Collator.PRIMARY);
if (usCollator.compare("abc", "ABC") == 0) {
System.out.println("Strings are equivalent");
}
For comparing String
s exactly once, the compare
method provides the best performance. When sorting a list of String
s however, it is generally necessary to compare each String
multiple times. In this case, CollationKey
s provide better performance. The CollationKey
class converts a String
to a series of bits that can be compared bitwise against other CollationKey
s. A CollationKey
is created by a Collator
object for a given String
.
CollationKey
s from different Collator
s can not be compared. See the class description for CollationKey
for an example using CollationKey
s.Modifier and Type | Field | Description |
---|---|---|
static final int |
CANONICAL_DECOMPOSITION |
Decomposition mode value. |
static final int |
FULL_DECOMPOSITION |
Decomposition mode value. |
static final int |
IDENTICAL |
Collator strength value. |
static final int |
NO_DECOMPOSITION |
Decomposition mode value. |
static final int |
PRIMARY |
Collator strength value. |
static final int |
SECONDARY |
Collator strength value. |
static final int |
TERTIARY |
Collator strength value. |
Modifier | Constructor | Description |
---|---|---|
protected |
Default constructor. |
Modifier and Type | Method | Description |
---|---|---|
Object |
clone() |
Overrides Cloneable |
int |
compare |
Compares its two arguments for order. |
abstract int |
compare |
Compares the source string to the target string according to the collation rules for this Collator. |
boolean |
equals |
Compares the equality of two Collators. |
boolean |
equals |
Convenience method for comparing the equality of two strings based on this Collator's collation rules. |
static Locale[] |
getAvailableLocales() |
Returns an array of all locales for which the getInstance methods of this class can return localized instances. |
abstract CollationKey |
getCollationKey |
Transforms the String into a series of bits that can be compared bitwise to other CollationKeys. |
int |
getDecomposition() |
Get the decomposition mode of this Collator. |
static Collator |
getInstance() |
Gets the Collator for the current default locale. |
static Collator |
getInstance |
Gets the Collator for the desired locale. |
int |
getStrength() |
Returns this Collator's strength property. |
abstract int |
hashCode() |
Generates the hash code for this Collator. |
void |
setDecomposition |
Set the decomposition mode of this Collator. |
void |
setStrength |
Sets this Collator's strength property. |
finalize, getClass, notify, notifyAll, toString, wait, wait, wait
reversed, thenComparing, thenComparing, thenComparing, thenComparingDouble, thenComparingInt, thenComparingLong
public static final int PRIMARY
public static final int SECONDARY
public static final int TERTIARY
public static final int IDENTICAL
public static final int NO_DECOMPOSITION
public static final int CANONICAL_DECOMPOSITION
CANONICAL_DECOMPOSITION corresponds to Normalization Form D as described in Unicode Standard Annex #15: Unicode Normalization Forms.
public static final int FULL_DECOMPOSITION
FULL_DECOMPOSITION corresponds to Normalization Form KD as described in Unicode Standard Annex #15: Unicode Normalization Forms.
protected Collator()
public static Collator getInstance()
Locale.getDefault()
.public static Collator getInstance(Locale desiredLocale)
ks
" and/or the "kk
" Unicode collation settings, this method will call setStrength(int) and/or setDecomposition(int) on the created instance, if the specified Unicode collation settings are recognized based on the following mappings: BCP 47 values for strength (ks) | Collator constants for strength |
---|---|
level1 | PRIMARY |
level2 | SECONDARY |
level3 | TERTIARY* |
identic | IDENTICAL |
BCP 47 values for normalization (kk) | Collator constants for decomposition |
true | CANONICAL_DECOMPOSITION |
false | NO_DECOMPOSITION* |
Collator
class may produce different instances based on the "co
" Unicode collation identifier in the desiredLocale
. For example: Collator.getInstance(Locale.forLanguageTag("sv-u-co-trad"));
Collator
instance with the Swedish traditional sorting, which gives 'v' and 'w' the same sorting order, while the Collator
instance for the Swedish locale without "co" identifier distinguishes 'v' and 'w'.desiredLocale
- the desired locale.public abstract int compare(String source, String target)
For a one time comparison, this method has the best performance. If a given String will be involved in multiple comparisons, CollationKey.compareTo has the best performance. See the Collator class description for an example using CollationKeys.
source
- the source string.target
- the target string.public int compare(Object o1, Object o2)
This implementation merely returns compare((String)o1, (String)o2)
.
compare
in interface Comparator<Object>
o1
- the first object to be compared.o2
- the second object to be compared.ClassCastException
- the arguments cannot be cast to Strings.public abstract CollationKey getCollationKey(String source)
source
- the string to be transformed into a collation key.public boolean equals(String source, String target)
source
- the source string to be compared with.target
- the target string to be compared with.public int getStrength()
public void setStrength(int newStrength)
newStrength
- the new strength value.IllegalArgumentException
- If the new strength value is not one of PRIMARY, SECONDARY, TERTIARY or IDENTICAL.public int getDecomposition()
The three values for decomposition mode are:
public void setDecomposition(int decompositionMode)
decompositionMode
- the new decomposition mode.IllegalArgumentException
- If the given value is not a valid decomposition mode.public static Locale[] getAvailableLocales()
getInstance
methods of this class can return localized instances. The returned array represents the union of locales supported by the Java runtime and by installed CollatorProvider
implementations. At a minimum, the returned array must contain a Locale
instance equal to Locale.ROOT
and a Locale
instance equal to Locale.US
.Collator
instances are available.public Object clone()
public boolean equals(Object that)
equals
in interface Comparator<Object>
equals
in class Object
that
- the Collator to be compared with this.public abstract int hashCode()
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https://docs.oracle.com/en/java/javase/21/docs/api/java.base/java/text/Collator.html