Collator

Class Overview

Performs locale-sensitive string comparison. A concrete subclass, RuleBasedCollator, allows customization of the collation ordering by the use of rule sets.

Following the Unicode Consortium's specifications for the Unicode Collation Algorithm (UCA), there are 4 different levels of strength used in comparisons:

• PRIMARY strength: Typically, this is used to denote differences between base characters (for example, "a" < "b"). It is the strongest difference. For example, dictionaries are divided into different sections by base character.
• SECONDARY strength: Accents in the characters are considered secondary differences (for example, "as" < "às" < "at"). Other differences between letters can also be considered secondary differences, depending on the language. A secondary difference is ignored when there is a primary difference anywhere in the strings.
• TERTIARY strength: Upper and lower case differences in characters are distinguished at tertiary strength (for example, "ao" < "Ao" < "aò"). In addition, a variant of a letter differs from the base form on the tertiary strength (such as "A" and "Ⓐ"). Another example is the difference between large and small Kana. A tertiary difference is ignored when there is a primary or secondary difference anywhere in the strings.
• IDENTICAL strength: When all other strengths are equal, the IDENTICAL strength is used as a tiebreaker. The Unicode code point values of the NFD form of each string are compared, just in case there is no difference. For example, Hebrew cantellation marks are only distinguished at this strength. This strength should be used sparingly, as only code point value differences between two strings are an extremely rare occurrence. Using this strength substantially decreases the performance for both comparison and collation key generation APIs. This strength also increases the size of the collation key.

This Collator deals only with two decomposition modes, the canonical decomposition mode and one that does not use any decomposition. The compatibility decomposition mode java.text.Collator.FULL_DECOMPOSITION is not supported here. If the canonical decomposition mode is set, Collator handles un-normalized text properly, producing the same results as if the text were normalized in NFD. If canonical decomposition is turned off, it is the user's responsibility to ensure that all text is already in the appropriate form before performing a comparison or before getting a CollationKey.

Examples:

 // 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");
 }
 

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();
 myCollator.setDecomposition(Collator.NO_DECOMPOSITION);
 if (myCollator.compare("ḁ̀", "ḁ̀") != 0) {
     System.out.println("ḁ̀ is not equal to ḁ̀ without decomposition");
     myCollator.setDecomposition(Collator.CANONICAL_DECOMPOSITION);
     if (myCollator.compare("ḁ̀", "ḁ̀") != 0) {
         System.out.println("Error: ḁ̀ should be equal to ḁ̀ with decomposition");
     } else {
         System.out.println("ḁ̀ is equal to ḁ̀ with decomposition");
     }
 } else {
     System.out.println("Error: ḁ̀ should be not equal to ḁ̀ without decomposition");
 }
 

Summary

[Expand] Inherited Methods
From class java.lang.Object Object clone() Creates and returns a copy of this Object. boolean equals(Object o) Compares this instance with the specified object and indicates if they are equal. void finalize() Called before the object's memory is reclaimed by the VM. final Class<? extends Object> getClass() Returns the unique instance of Class that represents this object's class. int hashCode() Returns an integer hash code for this object. final void notify() Causes a thread which is waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. final void notifyAll() Causes all threads which are waiting on this object's monitor (by means of calling one of the wait() methods) to be woken up. String toString() Returns a string containing a concise, human-readable description of this object. final void wait() Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object. final void wait(long millis, int nanos) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires. final void wait(long millis) Causes the calling thread to wait until another thread calls the notify() or notifyAll() method of this object or until the specified timeout expires.
From interface java.util.Comparator abstract int compare(T object1, T object2) Compares the two specified objects to determine their relative ordering. abstract boolean equals(Object object) Compares this Comparator with the specified Object and indicates whether they are equal.