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Class java.text.TableCollation

java.lang.Object
   |
   +----java.text.Collation
           |
           +----java.text.TableCollation

public class TableCollation
extends Collation

The TableCollation class provides the simple implementation of Collation, using data-driven tables. The user can create a customized table-based collation. TableCollation maps characters to sort keys.

Table Collation has the following restrictions for efficiency (other subclasses may be used for more complex languages) :

1. The French secondary ordering is applied to the whole collation object.

2. All non-mentioned Unicode characters are at the end of the collation order.

3. Private use characters are treated as identical. The private use area in Unicode is 0xE800-0xF8FF.

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 following demonstrates how to create your own collation rules:

Text Argument: A text argument is any sequence of characters, excluding special characters (that is, whitespace characters and the characters used in modifier, relation and reset). If those characters are desired, you can put them in single quotes (e.g. ampersand => '&').
Modifier: There is only a single modifier currently, which is used to specify that all accents (secondary differences) are backwards.
'@' : Indicates that accents are sorted backwards, as in French.
Relation: The relations are the following:
- '<' : Greater, as a letter difference (primary)
- ';' : Greater, as an accent difference (secondary)
- ',' : Greater, as a case difference (tertiary)
- '=' : Equal
Reset: There is only a single reset currently, which is used primarily for contractions and expansions, but which can also be used to add a modification at the end of a set of rules.
'&' : Indicates that the next rule follows the position to where the reset text-argument would be sorted. The reset does not put the text-argument into the sorting sequence.
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. (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 "ä" (a-umlaut) is treated as though it expands to two characters (expressed as "a & ae ; ä < 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
The Collation object automatically normalizes text internally to separate accents from base characters where possible. This is done both when processing the rules, and when comparing two strings. Collation also uses the Unicode canonical mapping to ensure that combining sequences are sorted properly (for more information, see The Unicode Standard, Version 2.0.)

Errors
The following are errors:
- A text-argument not preceded by either a reset or relation character (e.g. "a < b c < d").
- A relation or reset character not followed by a text-argument (e.g. "a < , b").
- A reset where the text-argument (or an initial substring of the text-argument) is not already in the sequence. (e.g. "a < b & e < f")
If you produce one of these errors, a FormatException will be thrown by TableCollation.
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 < å=a?,Å=A? ;aa,AA< æ,Æ< ø,Ø"
To create a table-based collation object, simply supply the collation rules to the TableCollation contructor. For example:
```
       TableCollation mySimple = new TableCollation(Simple);
 
```
Another example:
```
       TableCollation myNorwegian = new TableCollation(Norwegian);
 
```
To add rules on top of an existing table, simply supply the orginal rules and modifications to TableCollation constructor. For example,
Traditional Spanish (fragment): ... & C < ch , cH , Ch , CH ...
German (fragment) : ...< y , Y < z , Z & AE , A? & Ae ; a? & OE , O? & Oe ; o? & UE , U? & Ue ; u?
Symbols (fragment) : ...< y, Y < z , Z & Question-mark ; ? & Ampersand ; '&' & Dollar-sign ; $
To create a collation object for traditional Spanish, the user can take the English collation rules and add the additional rules to the table. For example:
```
       TableCollation mySpanish = new
           TableCollation(CollationRules.DEFAULTRULES +
                          "& C < ch, cH, Ch, CH");
 
```
In order to sort symbols in the similiar order of sorting their alphabetic equivalents, you can do the following,
```
       TableCollation myTable = new
           TableCollation(CollationRules.DEFAULTRULES +
                          "& Question-mark ; ?" +
                          "& Ampersand ; '&'" +
                          "& Dollar-sign ; $");
 
```
Another way of creating the table-based collation object, mySimple, is:
```
       TableCollation mySimple = new
           TableCollation(" < a < b & b < c & c < d");
 
```
Or,
```
       TableCollation mySimple = new
           TableCollation(" < a < b < d & b < c");
 
```
Because " < a < b < c < d" is the same as "a < b < d & b < c" or "< a < b & b < c & c < d".
NOTE: Typically, a collation object is created with Collation.getDefault().

See Also:
Collation, CollationElementIterator

TableCollation(String)
TableCollation constructor.

clone()
Standard override; no change in semantics.
compare(String, int, int, String, int, int)
Compares a range of character data stored in two different strings based on the collation rules.
compare(String, String)
Compares the character data stored in two different strings based on the collation rules.
equals(Object)
Compares the equality of two collation objects.
getCollationKey(String)
Transforms the string into a series of characters that can be compared with CollationKey.compareTo.
getCollationKey(String, int, int)
Transforms the string into a series of characters that can be compared with CollationKey.compareTo.
getRules()
Gets the table-based rules for the collation object.
getSortKey(String)
Transforms the string into a series of characters that can be compared with SortKey.compareTo.
getSortKey(String, int, int)
Transforms a specified region of the string into a series of characters that can be compared with SortKey.compareTo.
hashCode()
Generates the hash code for the table-based collation object

TableCollation
```
  public TableCollation(String rules) throws FormatException
```
TableCollation constructor. This takes the table rules and builds a collation table out of them. Please see TableCollation class description for more details on the collation rule syntax.

Parameters:
rules - the collation rules to build the collation table rom.
Throws: FormatException
A format exception will be thrown if the build process of the rules fails. For example, build rule "a < b c < d" will cause the ctor to throw a FormatException instance.
See Also:
LocaleData

getRules
```
  public String getRules()
```
Gets the table-based rules for the collation object.

Returns:
returns the collation rules that the table collation object was created from.

compare
```
  public byte 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.

Overrides:
compare in class Collation

compare
```
  public byte compare(String source,
                      int start,
                      int end,
                      String target,
                      int targetStart,
                      int targetEnd)
```
Compares a range of 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.

Throws: StringIndexOutOfBoundsException
If the starting offset of a string is greater than the ending offset.
Overrides:
compare in class Collation

getSortKey
```
  public SortKey getSortKey(String source)
```
Transforms the string into a series of characters that can be compared with SortKey.compareTo. This overrides java.util.Collation.getSortKey. It can be overriden in a subclass.

Overrides:
getSortKey in class Collation

getSortKey
```
  public SortKey getSortKey(String source,
                            int start,
                            int end)
```
Transforms a specified region of the string into a series of characters that can be compared with SortKey.compareTo. This overrides java.util.Collation.getSortKey. It can be overriden in a subclass.

Overrides:
getSortKey in class Collation

getCollationKey
```
  public CollationKey getCollationKey(String source)
```
Transforms the string into a series of characters that can be compared with CollationKey.compareTo. Handles indefinite number of ignorable characters. The collation keys must be compared with CollationKey.compareTo. It can be overriden in a subclass.

Overrides:
getCollationKey in class Collation

getCollationKey
```
  public CollationKey getCollationKey(String source,
                                      int start,
                                      int end)
```
Transforms the string into a series of characters that can be compared with CollationKey.compareTo. Handles indefinite number of ignorable characters of the specified range of the source string. It can be overriden in a subclass.

Overrides:
getCollationKey in class Collation

clone
```
  public Object clone()
```
Standard override; no change in semantics.

Overrides:
clone in class Collation

equals
```
  public boolean equals(Object obj)
```
Compares the equality of two collation objects.

Parameters:
obj - the table-based collation object to be compared with this.
Returns:
true if the current table-based collation object is the same as the table-based collation object obj; false otherwise.
Overrides:
equals in class Collation

hashCode
```
  public int hashCode()
```
Generates the hash code for the table-based collation object

Overrides:
hashCode in class Collation
```
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