Class Transliterator
- All Implemented Interfaces:
StringTransform
,Transform<String,
String>
- Direct Known Subclasses:
RuleBasedTransliterator
Transliterator
is an abstract class that transliterates text from one format to another. The most common
kind of transliterator is a script, or alphabet, transliterator. For example, a Russian to Latin transliterator
changes Russian text written in Cyrillic characters to phonetically equivalent Latin characters. It does not
translate Russian to English! Transliteration, unlike translation, operates on characters, without reference
to the meanings of words and sentences.
Although script conversion is its most common use, a transliterator can actually perform a more general class of
tasks. In fact, Transliterator
defines a very general API which specifies only that a segment of the
input text is replaced by new text. The particulars of this conversion are determined entirely by subclasses of
Transliterator
.
Transliterators are stateless
Transliterator
objects are stateless; they retain no information between calls to
transliterate()
. As a result, threads may share transliterators without synchronizing them. This might
seem to limit the complexity of the transliteration operation. In practice, subclasses perform complex
transliterations by delaying the replacement of text until it is known that no other replacements are possible. In
other words, although the Transliterator
objects are stateless, the source text itself embodies all the
needed information, and delayed operation allows arbitrary complexity.
Batch transliteration
The simplest way to perform transliteration is all at once, on a string of existing text. This is referred to as
batch transliteration. For example, given a string input
and a transliterator t
,
the call
String result = t.transliterate(input);
will transliterate it and return the result. Other methods allow the client to specify a substring to be
transliterated and to use Replaceable
objects instead of strings, in order to preserve out-of-band
information (such as text styles).
Keyboard transliteration
Somewhat more involved is keyboard, or incremental transliteration. This is the transliteration of text that is arriving from some source (typically the user's keyboard) one character at a time, or in some other piecemeal fashion.
In keyboard transliteration, a Replaceable
buffer stores the text. As text is inserted, as much as
possible is transliterated on the fly. This means a GUI that displays the contents of the buffer may show text being
modified as each new character arrives.
Consider the simple rule-based Transliterator:
th>{theta}
t>{tau}
When the user types 't', nothing will happen, since the transliterator is waiting to see if the next character is
'h'. To remedy this, we introduce the notion of a cursor, marked by a '|' in the output string:
t>|{tau}
{tau}h>{theta}
Now when the user types 't', tau appears, and if the next character is 'h', the tau changes to a theta. This is
accomplished by maintaining a cursor position (independent of the insertion point, and invisible in the GUI) across
calls to transliterate()
. Typically, the cursor will be coincident with the insertion point, but in a
case like the one above, it will precede the insertion point.
Keyboard transliteration methods maintain a set of three indices that are updated with each call to
transliterate()
, including the cursor, start, and limit. These indices are changed by the method, and
they are passed in and out via a Position object. The start
index marks the beginning of the substring
that the transliterator will look at. It is advanced as text becomes committed (but it is not the committed index;
that's the cursor
). The cursor
index, described above, marks the point at which the
transliterator last stopped, either because it reached the end, or because it required more characters to
disambiguate between possible inputs. The cursor
can also be explicitly set by rules.
Any characters before the cursor
index are frozen; future keyboard
transliteration calls within this input sequence will not change them. New text is inserted at the limit
index, which marks the end of the substring that the transliterator looks at.
Because keyboard transliteration assumes that more characters are to arrive, it is conservative in its operation. It
only transliterates when it can do so unambiguously. Otherwise it waits for more characters to arrive. When the
client code knows that no more characters are forthcoming, perhaps because the user has performed some input
termination operation, then it should call finishTransliteration()
to complete any pending
transliterations.
Inverses
Pairs of transliterators may be inverses of one another. For example, if transliterator A transliterates
characters by incrementing their Unicode value (so "abc" -> "def"), and transliterator B decrements character
values, then A is an inverse of B and vice versa. If we compose A with B in a compound
transliterator, the result is the identity transliterator, that is, a transliterator that does not change its input
text.
The Transliterator
method getInverse()
returns a transliterator's inverse, if one exists,
or null
otherwise. However, the result of getInverse()
usually will not be a true
mathematical inverse. This is because true inverse transliterators are difficult to formulate. For example, consider
two transliterators: AB, which transliterates the character 'A' to 'B', and BA, which transliterates
'B' to 'A'. It might seem that these are exact inverses, since
"A" x AB -> "B"where 'x' represents transliteration. However,
"B" x BA -> "A"
"ABCD" x AB -> "BBCD"so AB composed with BA is not the identity. Nonetheless, BA may be usefully considered to be AB's inverse, and it is on this basis that AB
"BBCD" x BA -> "AACD"
.getInverse()
could legitimately return
BA.
Filtering
Each transliterator has a filter, which restricts changes to those characters selected by the filter. The filter affects just the characters that are changed -- the characters outside of the filter are still part of the context for the filter. For example, in the following even though 'x' is filtered out, and doesn't convert to y, it does affect the conversion of 'a'.
String rules = "x > y; x{a} > b; "; Transliterator tempTrans = Transliterator.createFromRules("temp", rules, Transliterator.FORWARD); tempTrans.setFilter(new UnicodeSet("[a]")); String tempResult = tempTrans.transform("xa"); // results in "xb"
IDs and display names
A transliterator is designated by a short identifier string or ID. IDs follow the format source-destination, where source describes the entity being replaced, and destination describes the entity replacing source. The entities may be the names of scripts, particular sequences of characters, or whatever else it is that the transliterator converts to or from. For example, a transliterator from Russian to Latin might be named "Russian-Latin". A transliterator from keyboard escape sequences to Latin-1 characters might be named "KeyboardEscape-Latin1". By convention, system entity names are in English, with the initial letters of words capitalized; user entity names may follow any format so long as they do not contain dashes.
In addition to programmatic IDs, transliterator objects have display names for presentation in user interfaces,
returned by getDisplayName(java.lang.String)
.
Factory methods and registration
In general, client code should use the factory method getInstance()
to obtain an instance of a
transliterator given its ID. Valid IDs may be enumerated using getAvailableIDs()
. Since transliterators
are stateless, multiple calls to getInstance()
with the same ID will return the same object.
In addition to the system transliterators registered at startup, user transliterators may be registered by calling
registerInstance()
at run time. To register a transliterator subclass without instantiating it (until it
is needed), users may call registerClass()
.
Composed transliterators
In addition to built-in system transliterators like "Latin-Greek", there are also built-in composed transliterators. These are implemented by composing two or more component transliterators. For example, if we have scripts "A", "B", "C", and "D", and we want to transliterate between all pairs of them, then we need to write 12 transliterators: "A-B", "A-C", "A-D", "B-A",..., "D-A", "D-B", "D-C". If it is possible to convert all scripts to an intermediate script "M", then instead of writing 12 rule sets, we only need to write 8: "A~M", "B~M", "C~M", "D~M", "M~A", "M~B", "M~C", "M~D". (This might not seem like a big win, but it's really 2n vs. n 2 - n, so as n gets larger the gain becomes significant. With 9 scripts, it's 18 vs. 72 rule sets, a big difference.) Note the use of "~" rather than "-" for the script separator here; this indicates that the given transliterator is intended to be composed with others, rather than be used as is.
Composed transliterators can be instantiated as usual. For example, the system transliterator "Devanagari-Gujarati" is a composed transliterator built internally as "Devanagari~InterIndic;InterIndic~Gujarati". When this transliterator is instantiated, it appears externally to be a standard transliterator (e.g., getID() returns "Devanagari-Gujarati").
Subclassing
Subclasses must implement the abstract method handleTransliterate()
.
Subclasses should override the transliterate()
method taking a Replaceable
and the
transliterate()
method taking a String
and StringBuffer
if the performance of
these methods can be improved over the performance obtained by the default implementations in this class.
Rule syntax
A set of rules determines how to perform translations. Rules within a rule set are separated by semicolons (';'). To include a literal semicolon, prefix it with a backslash ('\'). Unicode Pattern_White_Space is ignored. If the first non-blank character on a line is '#', the entire line is ignored as a comment.
Each set of rules consists of two groups, one forward, and one reverse. This is a convention that is not enforced; rules for one direction may be omitted, with the result that translations in that direction will not modify the source text. In addition, bidirectional forward-reverse rules may be specified for symmetrical transformations.
Note: Another description of the Transliterator rule syntax is available in section Transform Rules Syntax of UTS #35: Unicode LDML. The rules are shown there using arrow symbols ← and → and ↔. ICU supports both those and the equivalent ASCII symbols < and > and <>.
Rule statements take one of the following forms:
$alefmadda=\\u0622;
- Variable definition. The name on the
left is assigned the text on the right. In this example,
after this statement, instances of the left hand name,
"
$alefmadda
", will be replaced by the Unicode character U+0622. Variable names must begin with a letter and consist only of letters, digits, and underscores. Case is significant. Duplicate names cause an exception to be thrown, that is, variables cannot be redefined. The right hand side may contain well-formed text of any length, including no text at all ("$empty=;
"). The right hand side may contain embeddedUnicodeSet
patterns, for example, "$softvowel=[eiyEIY]
". ai>$alefmadda;
- Forward translation rule. This rule states that the string on the left will be changed to the string on the right when performing forward transliteration.
ai<$alefmadda;
- Reverse translation rule. This rule states that the string on the right will be changed to the string on the left when performing reverse transliteration.
ai<>$alefmadda;
- Bidirectional translation rule. This rule states that the string on the right will be changed to the string on the left when performing forward transliteration, and vice versa when performing reverse transliteration.
Translation rules consist of a match pattern and an output
string. The match pattern consists of literal characters,
optionally preceded by context, and optionally followed by
context. Context characters, like literal pattern characters,
must be matched in the text being transliterated. However, unlike
literal pattern characters, they are not replaced by the output
text. For example, the pattern "abc{def}
"
indicates the characters "def
" must be
preceded by "abc
" for a successful match.
If there is a successful match, "def
" will
be replaced, but not "abc
". The final '}
'
is optional, so "abc{def
" is equivalent to
"abc{def}
". Another example is "{123}456
"
(or "123}456
") in which the literal
pattern "123
" must be followed by "456
".
The output string of a forward or reverse rule consists of
characters to replace the literal pattern characters. If the
output string contains the character '|
', this is
taken to indicate the location of the cursor after
replacement. The cursor is the point in the text at which the
next replacement, if any, will be applied. The cursor is usually
placed within the replacement text; however, it can actually be
placed into the precending or following context by using the
special character '@'. Examples:
a {foo} z > | @ bar; # foo -> bar, move cursor before a {foo} xyz > bar @@|; # foo -> bar, cursor between y and z
UnicodeSet
UnicodeSet
patterns may appear anywhere that
makes sense. They may appear in variable definitions.
Contrariwise, UnicodeSet
patterns may themselves
contain variable references, such as "$a=[a-z];$not_a=[^$a]
",
or "$range=a-z;$ll=[$range]
".
UnicodeSet
patterns may also be embedded directly
into rule strings. Thus, the following two rules are equivalent:
$vowel=[aeiou]; $vowel>'*'; # One way to do this [aeiou]>'*'; # Another way
See UnicodeSet
for more documentation and examples.
Segments
Segments of the input string can be matched and copied to the output string. This makes certain sets of rules simpler and more general, and makes reordering possible. For example:
([a-z]) > $1 $1; # double lowercase letters ([:Lu:]) ([:Ll:]) > $2 $1; # reverse order of Lu-Ll pairs
The segment of the input string to be copied is delimited by
"(
" and ")
". Up to
nine segments may be defined. Segments may not overlap. In the
output string, "$1
" through "$9
"
represent the input string segments, in left-to-right order of
definition.
Anchors
Patterns can be anchored to the beginning or the end of the text. This is done with the
special characters '^
' and '$
'. For example:
^ a > 'BEG_A'; # match 'a' at start of text a > 'A'; # match other instances of 'a' z $ > 'END_Z'; # match 'z' at end of text z > 'Z'; # match other instances of 'z'
It is also possible to match the beginning or the end of the text using a UnicodeSet
.
This is done by including a virtual anchor character '$
' at the end of the
set pattern. Although this is usually the match character for the end anchor, the set will
match either the beginning or the end of the text, depending on its placement. For
example:
$x = [a-z$]; # match 'a' through 'z' OR anchor $x 1 > 2; # match '1' after a-z or at the start 3 $x > 4; # match '3' before a-z or at the end
Example
The following example rules illustrate many of the features of the rule language.
Rule 1. | abc{def}>x|y |
Rule 2. | xyz>r |
Rule 3. | yz>q |
Applying these rules to the string "adefabcdefz
"
yields the following results:
|adefabcdefz |
Initial state, no rules match. Advance cursor. |
a|defabcdefz |
Still no match. Rule 1 does not match because the preceding context is not present. |
ad|efabcdefz |
Still no match. Keep advancing until there is a match... |
ade|fabcdefz |
... |
adef|abcdefz |
... |
adefa|bcdefz |
... |
adefab|cdefz |
... |
adefabc|defz |
Rule 1 matches; replace "def "
with "xy " and back up the cursor
to before the 'y '. |
adefabcx|yz |
Although "xyz " is
present, rule 2 does not match because the cursor is
before the 'y ', not before the 'x '.
Rule 3 does match. Replace "yz "
with "q ". |
adefabcxq| |
The cursor is at the end; transliteration is complete. |
The order of rules is significant. If multiple rules may match at some point, the first matching rule is applied.
Forward and reverse rules may have an empty output string. Otherwise, an empty left or right hand side of any statement is a syntax error.
Single quotes are used to quote any character other than a
digit or letter. To specify a single quote itself, inside or
outside of quotes, use two single quotes in a row. For example,
the rule "'>'>o''clock
" changes the
string ">
" to the string "o'clock
".
Notes
While a Transliterator is being built from rules, it checks that the rules are added in proper order. For example, if the rule "a>x" is followed by the rule "ab>y", then the second rule will throw an exception. The reason is that the second rule can never be triggered, since the first rule always matches anything it matches. In other words, the first rule masks the second rule.
- Author:
- Alan Liu
-
Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic interface
The factory interface for transliterators.static class
Position structure for incremental transliteration. -
Field Summary
FieldsModifier and TypeFieldDescriptionstatic final int
Direction constant indicating the forward direction in a transliterator, e.g., the forward rules of a rule-based Transliterator.static final int
Direction constant indicating the reverse direction in a transliterator, e.g., the reverse rules of a rule-based Transliterator. -
Constructor Summary
ConstructorsModifierConstructorDescriptionprotected
Transliterator
(String ID, UnicodeFilter filter) Default constructor. -
Method Summary
Modifier and TypeMethodDescriptionvoid
addSourceTargetSet
(UnicodeSet inputFilter, UnicodeSet sourceSet, UnicodeSet targetSet) Deprecated.This API is ICU internal only.protected final String
baseToRules
(boolean escapeUnprintable) Returns a rule string for this transliterator.static final Transliterator
createFromRules
(String ID, String rules, int dir) Returns aTransliterator
object constructed from the given rule string.void
filteredTransliterate
(Replaceable text, Transliterator.Position index, boolean incremental) Transliterate a substring of text, as specified by index, taking filters into account.final void
finishTransliteration
(Replaceable text, Transliterator.Position index) Finishes any pending transliterations that were waiting for more characters.static final Enumeration
<String> Returns an enumeration over the programmatic names of registeredTransliterator
objects.static final Enumeration
<String> Returns an enumeration over the source names of registered transliterators.static final Enumeration
<String> getAvailableTargets
(String source) Returns an enumeration over the target names of registered transliterators having a given source name.static final Enumeration
<String> getAvailableVariants
(String source, String target) Returns an enumeration over the variant names of registered transliterators having a given source name and target name.static final String
getDisplayName
(String ID) Returns a name for this transliterator that is appropriate for display to the user in the defaultDISPLAY
locale.static String
getDisplayName
(String id, ULocale inLocale) Returns a name for this transliterator that is appropriate for display to the user in the given locale.static String
getDisplayName
(String id, Locale inLocale) Returns a name for this transliterator that is appropriate for display to the user in the given locale.Return the elements that make up this transliterator.final UnicodeFilter
Returns the filter used by this transliterator, or null if this transliterator uses no filter.getFilterAsUnicodeSet
(UnicodeSet externalFilter) Deprecated.This API is ICU internal only.final String
getID()
Returns a programmatic identifier for this transliterator.static final Transliterator
getInstance
(String ID) Returns aTransliterator
object given its ID.static Transliterator
getInstance
(String ID, int dir) Returns aTransliterator
object given its ID.final Transliterator
Returns this transliterator's inverse.final int
Returns the length of the longest context required by this transliterator.final UnicodeSet
Returns the set of all characters that may be modified in the input text by this Transliterator.Returns the set of all characters that may be generated as replacement text by this transliterator.protected UnicodeSet
Framework method that returns the set of all characters that may be modified in the input text by this Transliterator, ignoring the effect of this object's filter.protected abstract void
handleTransliterate
(Replaceable text, Transliterator.Position pos, boolean incremental) Abstract method that concrete subclasses define to implement their transliteration algorithm.static void
registerAlias
(String aliasID, String realID) Register an ID as an alias of another ID.static void
Deprecated.This API is ICU internal only.static void
registerClass
(String ID, Class<? extends Transliterator> transClass, String displayName) Registers a subclass ofTransliterator
with the system.static void
registerFactory
(String ID, Transliterator.Factory factory) Register a factory object with the given ID.static void
registerInstance
(Transliterator trans) Register a Transliterator object with the given ID.void
setFilter
(UnicodeFilter filter) Changes the filter used by this transliterator.protected final void
Set the programmatic identifier for this transliterator.protected void
setMaximumContextLength
(int a) Method for subclasses to use to set the maximum context length.toRules
(boolean escapeUnprintable) Returns a rule string for this transliterator.Implements StringTransform via this method.final void
transliterate
(Replaceable text) Transliterates an entire string in place.final int
transliterate
(Replaceable text, int start, int limit) Transliterates a segment of a string, with optional filtering.final void
transliterate
(Replaceable text, Transliterator.Position index) Transliterates the portion of the text buffer that can be transliterated unambiguosly.final void
transliterate
(Replaceable text, Transliterator.Position index, int insertion) Transliterates the portion of the text buffer that can be transliterated unambiguosly after a new character has been inserted, typically as a result of a keyboard event.final void
transliterate
(Replaceable text, Transliterator.Position index, String insertion) Transliterates the portion of the text buffer that can be transliterated unambiguosly after new text has been inserted, typically as a result of a keyboard event.final String
transliterate
(String text) Transliterate an entire string and returns the result.static void
unregister
(String ID) Unregisters a transliterator or class.
-
Field Details
-
FORWARD
public static final int FORWARDDirection constant indicating the forward direction in a transliterator, e.g., the forward rules of a rule-based Transliterator. An "A-B" transliterator transliterates A to B when operating in the forward direction, and B to A when operating in the reverse direction.- See Also:
-
REVERSE
public static final int REVERSEDirection constant indicating the reverse direction in a transliterator, e.g., the reverse rules of a rule-based Transliterator. An "A-B" transliterator transliterates A to B when operating in the forward direction, and B to A when operating in the reverse direction.- See Also:
-
-
Constructor Details
-
Transliterator
Default constructor.- Parameters:
ID
- the string identifier for this transliteratorfilter
- the filter. Any character for which filter.contains() returns false will not be altered by this transliterator. If filter is null then no filtering is applied.
-
-
Method Details
-
transliterate
Transliterates a segment of a string, with optional filtering.- Parameters:
text
- the string to be transliteratedstart
- the beginning index, inclusive;0 <= start <= limit
.limit
- the ending index, exclusive;start <= limit <= text.length()
.- Returns:
- The new limit index. The text previously occupying
[start, limit)
has been transliterated, possibly to a string of a different length, at[start,
new-limit)
, where new-limit is the return value. If the input offsets are out of bounds, the returned value is -1 and the input string remains unchanged.
-
transliterate
Transliterates an entire string in place. Convenience method.- Parameters:
text
- the string to be transliterated
-
transliterate
Transliterate an entire string and returns the result. Convenience method.- Parameters:
text
- the string to be transliterated- Returns:
- The transliterated text
-
transliterate
Transliterates the portion of the text buffer that can be transliterated unambiguosly after new text has been inserted, typically as a result of a keyboard event. The new text ininsertion
will be inserted intotext
atindex.contextLimit
, advancingindex.contextLimit
byinsertion.length()
. Then the transliterator will try to transliterate characters oftext
betweenindex.start
andindex.contextLimit
. Characters beforeindex.start
will not be changed.Upon return, values in
index
will be updated.index.contextStart
will be advanced to the first character that future calls to this method will read.index.start
andindex.contextLimit
will be adjusted to delimit the range of text that future calls to this method may change.Typical usage of this method begins with an initial call with
index.contextStart
andindex.contextLimit
set to indicate the portion oftext
to be transliterated, andindex.start == index.contextStart
. Thereafter,index
can be used without modification in future calls, provided that all changes totext
are made via this method.This method assumes that future calls may be made that will insert new text into the buffer. As a result, it only performs unambiguous transliterations. After the last call to this method, there may be untransliterated text that is waiting for more input to resolve an ambiguity. In order to perform these pending transliterations, clients should call
finishTransliteration(com.ibm.icu.text.Replaceable, com.ibm.icu.text.Transliterator.Position)
after the last call to this method has been made.- Parameters:
text
- the buffer holding transliterated and untransliterated textindex
- the start and limit of the text, the position of the cursor, and the start and limit of transliteration.insertion
- text to be inserted and possibly transliterated into the translation buffer atindex.contextLimit
. Ifnull
then no text is inserted.- Throws:
IllegalArgumentException
- ifindex
is invalid- See Also:
-
transliterate
Transliterates the portion of the text buffer that can be transliterated unambiguosly after a new character has been inserted, typically as a result of a keyboard event. This is a convenience method; seetransliterate(Replaceable, Transliterator.Position, String)
for details.- Parameters:
text
- the buffer holding transliterated and untransliterated textindex
- the start and limit of the text, the position of the cursor, and the start and limit of transliteration.insertion
- text to be inserted and possibly transliterated into the translation buffer atindex.contextLimit
.- See Also:
-
transliterate
Transliterates the portion of the text buffer that can be transliterated unambiguosly. This is a convenience method; seetransliterate(Replaceable, Transliterator.Position, String)
for details.- Parameters:
text
- the buffer holding transliterated and untransliterated textindex
- the start and limit of the text, the position of the cursor, and the start and limit of transliteration.- See Also:
-
finishTransliteration
Finishes any pending transliterations that were waiting for more characters. Clients should call this method as the last call after a sequence of one or more calls totransliterate()
.- Parameters:
text
- the buffer holding transliterated and untransliterated text.index
- the array of indices previously passed totransliterate(com.ibm.icu.text.Replaceable, int, int)
-
handleTransliterate
protected abstract void handleTransliterate(Replaceable text, Transliterator.Position pos, boolean incremental) Abstract method that concrete subclasses define to implement their transliteration algorithm. This method handles both incremental and non-incremental transliteration. LetoriginalStart
refer to the value ofpos.start
upon entry.- If
incremental
is false, then this method should transliterate all characters betweenpos.start
andpos.limit
. Upon returnpos.start
must ==pos.limit
. - If
incremental
is true, then this method should transliterate all characters betweenpos.start
andpos.limit
that can be unambiguously transliterated, regardless of future insertions of text atpos.limit
. Upon return,pos.start
should be in the range [originalStart
,pos.limit
).pos.start
should be positioned such that characters [originalStart
,pos.start
) will not be changed in the future by this transliterator and characters [pos.start
,pos.limit
) are unchanged.
Implementations of this method should also obey the following invariants:
-
pos.limit
andpos.contextLimit
should be updated to reflect changes in length of the text betweenpos.start
andpos.limit
. The differencepos.contextLimit - pos.limit
should not change. pos.contextStart
should not change.- Upon return, neither
pos.start
norpos.limit
should be less thanoriginalStart
. - Text before
originalStart
and text afterpos.limit
should not change. - Text before
pos.contextStart
and text afterpos.contextLimit
should be ignored.
Subclasses may safely assume that all characters in [
pos.start
,pos.limit
) are filtered. In other words, the filter has already been applied by the time this method is called. SeefilteredTransliterate()
.This method is not for public consumption. Calling this method directly will transliterate [
pos.start
,pos.limit
) without applying the filter. End user code should calltransliterate()
instead of this method. Subclass code should callfilteredTransliterate()
instead of this method.- Parameters:
text
- the buffer holding transliterated and untransliterated textpos
- the indices indicating the start, limit, context start, and context limit of the text.incremental
- if true, assume more text may be inserted atpos.limit
and act accordingly. Otherwise, transliterate all text betweenpos.start
andpos.limit
and movepos.start
up topos.limit
.- See Also:
- If
-
filteredTransliterate
public void filteredTransliterate(Replaceable text, Transliterator.Position index, boolean incremental) Transliterate a substring of text, as specified by index, taking filters into account. This method is for subclasses that need to delegate to another transliterator.- Parameters:
text
- the text to be transliteratedindex
- the position indicesincremental
- if true, then assume more characters may be inserted at index.limit, and postpone processing to accommodate future incoming characters
-
getMaximumContextLength
public final int getMaximumContextLength()Returns the length of the longest context required by this transliterator. This is preceding context. The default value is zero, but subclasses can change this by callingsetMaximumContextLength()
. For example, if a transliterator translates "ddd" (where d is any digit) to "555" when preceded by "(ddd)", then the preceding context length is 5, the length of "(ddd)".- Returns:
- The maximum number of preceding context characters this transliterator needs to examine
-
setMaximumContextLength
protected void setMaximumContextLength(int a) Method for subclasses to use to set the maximum context length.- See Also:
-
getID
Returns a programmatic identifier for this transliterator. If this identifier is passed togetInstance()
, it will return this object, if it has been registered.- See Also:
-
setID
Set the programmatic identifier for this transliterator. Only for use by subclasses. -
getDisplayName
Returns a name for this transliterator that is appropriate for display to the user in the defaultDISPLAY
locale. SeegetDisplayName(String,Locale)
for details.- See Also:
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getDisplayName
Returns a name for this transliterator that is appropriate for display to the user in the given locale. This name is taken from the locale resource data in the standard manner of thejava.text
package.If no localized names exist in the system resource bundles, a name is synthesized using a localized
MessageFormat
pattern from the resource data. The arguments to this pattern are an integer followed by one or two strings. The integer is the number of strings, either 1 or 2. The strings are formed by splitting the ID for this transliterator at the first '-'. If there is no '-', then the entire ID forms the only string.- Parameters:
inLocale
- the Locale in which the display name should be localized.- See Also:
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getDisplayName
Returns a name for this transliterator that is appropriate for display to the user in the given locale. This name is taken from the locale resource data in the standard manner of thejava.text
package.If no localized names exist in the system resource bundles, a name is synthesized using a localized
MessageFormat
pattern from the resource data. The arguments to this pattern are an integer followed by one or two strings. The integer is the number of strings, either 1 or 2. The strings are formed by splitting the ID for this transliterator at the first '-'. If there is no '-', then the entire ID forms the only string.- Parameters:
inLocale
- the ULocale in which the display name should be localized.- See Also:
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getFilter
Returns the filter used by this transliterator, or null if this transliterator uses no filter. -
setFilter
Changes the filter used by this transliterator. If the filter is set to null then no filtering will occur.Callers must take care if a transliterator is in use by multiple threads. The filter should not be changed by one thread while another thread may be transliterating.
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getInstance
Returns aTransliterator
object given its ID. The ID must be either a system transliterator ID or a ID registered usingregisterClass()
.- Parameters:
ID
- a valid ID, as enumerated bygetAvailableIDs()
- Returns:
- A
Transliterator
object with the given ID - Throws:
IllegalArgumentException
- if the given ID is invalid.
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getInstance
Returns aTransliterator
object given its ID. The ID must be either a system transliterator ID or a ID registered usingregisterClass()
.- Parameters:
ID
- a valid ID, as enumerated bygetAvailableIDs()
dir
- either FORWARD or REVERSE. If REVERSE then the inverse of the given ID is instantiated.- Returns:
- A
Transliterator
object with the given ID - Throws:
IllegalArgumentException
- if the given ID is invalid.- See Also:
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createFromRules
Returns aTransliterator
object constructed from the given rule string. This will be a rule-based Transliterator, if the rule string contains only rules, or a compound Transliterator, if it contains ID blocks, or a null Transliterator, if it contains ID blocks which parse as empty for the given direction.- Parameters:
ID
- the id for the transliterator.rules
- rules, separated by ';'dir
- either FORWARD or REVERSE.- Returns:
- a newly created Transliterator
- Throws:
IllegalArgumentException
- if there is a problem with the ID or the rules
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toRules
Returns a rule string for this transliterator.- Parameters:
escapeUnprintable
- if true, then unprintable characters will be converted to escape form backslash-'u' or backslash-'U'.
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baseToRules
Returns a rule string for this transliterator. This is a non-overrideable base class implementation that subclasses may call. It simply munges the ID into the correct format, that is, "foo" => "::foo".- Parameters:
escapeUnprintable
- if true, then unprintable characters will be converted to escape form backslash-'u' or backslash-'U'.
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getElements
Return the elements that make up this transliterator. For example, if the transliterator "NFD;Jamo-Latin;Latin-Greek" were created, the return value of this method would be an array of the three transliterator objects that make up that transliterator: [NFD, Jamo-Latin, Latin-Greek].If this transliterator is not composed of other transliterators, then this method will return an array of length one containing a reference to this transliterator.
- Returns:
- an array of one or more transliterators that make up this transliterator
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getSourceSet
Returns the set of all characters that may be modified in the input text by this Transliterator. This incorporates this object's current filter; if the filter is changed, the return value of this function will change. The default implementation returns an empty set. Some subclasses may overridehandleGetSourceSet()
to return a more precise result. The return result is approximate in any case and is intended for use by tests, tools, or utilities.- See Also:
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handleGetSourceSet
Framework method that returns the set of all characters that may be modified in the input text by this Transliterator, ignoring the effect of this object's filter. The base class implementation returns the empty set. Subclasses that wish to implement this should override this method.- Returns:
- the set of characters that this transliterator may modify. The set may be modified, so subclasses should return a newly-created object.
- See Also:
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getTargetSet
Returns the set of all characters that may be generated as replacement text by this transliterator. The default implementation returns the empty set. Some subclasses may override this method to return a more precise result. The return result is approximate in any case and is intended for use by tests, tools, or utilities requiring such meta-information.Warning. You might expect an empty filter to always produce an empty target. However, consider the following:
[Pp]{}[ΣςσϷϸϺϻ] > \';
With a filter of [], you still get some elements in the target set, because this rule will still match. It could be recast to the following if it were important.[Pp]{([ΣςσϷϸϺϻ])} > \' | $1;
- See Also:
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addSourceTargetSet
@Deprecated public void addSourceTargetSet(UnicodeSet inputFilter, UnicodeSet sourceSet, UnicodeSet targetSet) Deprecated.This API is ICU internal only.Returns the set of all characters that may be generated as replacement text by this transliterator, filtered by BOTH the input filter, and the current getFilter().SHOULD BE OVERRIDDEN BY SUBCLASSES. It is probably an error for any transliterator to NOT override this, but we can't force them to for backwards compatibility.
Other methods vector through this.
When gathering the information on source and target, the compound transliterator makes things complicated. For example, suppose we have:
Global FILTER = [ax] a > b; :: NULL; b > c; x > d;
While the filter just allows a and x, b is an intermediate result, which could produce c. So the source and target sets cannot be gathered independently. What we have to do is filter the sources for the first transliterator according to the global filter, intersect that transliterator's filter. Based on that we get the target. The next transliterator gets as a global filter (global + last target). And so on.There is another complication:
Global FILTER = [ax] a >|b; b >c;
Even though b would be filtered from the input, whenever we have a backup, it could be part of the input. So ideally we will change the global filter as we go.- Parameters:
targetSet
- TODO- See Also:
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getFilterAsUnicodeSet
Deprecated.This API is ICU internal only.Returns the intersectionof this instance's filter intersected with an external filter. The externalFilter must be frozen (it is frozen if not). The result may be frozen, so don't attempt to modify. -
getInverse
Returns this transliterator's inverse. See the class documentation for details. This implementation simply inverts the two entities in the ID and attempts to retrieve the resulting transliterator. That is, ifgetID()
returns "A-B", then this method will return the result ofgetInstance("B-A")
, ornull
if that call fails.Subclasses with knowledge of their inverse may wish to override this method.
- Returns:
- a transliterator that is an inverse, not necessarily
exact, of this transliterator, or
null
if no such transliterator is registered. - See Also:
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registerClass
public static void registerClass(String ID, Class<? extends Transliterator> transClass, String displayName) Registers a subclass ofTransliterator
with the system. This subclass must have a public constructor taking no arguments. When that constructor is called, the resulting object must return theID
passed to this method if itsgetID()
method is called.- Parameters:
ID
- the result ofgetID()
for this transliteratortransClass
- a subclass ofTransliterator
- See Also:
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registerFactory
Register a factory object with the given ID. The factory method should return a new instance of the given transliterator.Because ICU may choose to cache Transliterator objects internally, this must be called at application startup, prior to any calls to Transliterator.getInstance to avoid undefined behavior.
- Parameters:
ID
- the ID of this transliteratorfactory
- the factory object
-
registerInstance
Register a Transliterator object with the given ID.Because ICU may choose to cache Transliterator objects internally, this must be called at application startup, prior to any calls to Transliterator.getInstance to avoid undefined behavior.
- Parameters:
trans
- the Transliterator object
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registerAlias
Register an ID as an alias of another ID. Instantiating alias ID produces the same result as instantiating the original ID. This is generally used to create short aliases of compound IDs.Because ICU may choose to cache Transliterator objects internally, this must be called at application startup, prior to any calls to Transliterator.getInstance to avoid undefined behavior.
- Parameters:
aliasID
- The new ID being registered.realID
- The existing ID that the new ID should be an alias of.
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unregister
Unregisters a transliterator or class. This may be either a system transliterator or a user transliterator or class.- Parameters:
ID
- the ID of the transliterator or class- See Also:
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getAvailableIDs
Returns an enumeration over the programmatic names of registeredTransliterator
objects. This includes both system transliterators and user transliterators registered usingregisterClass()
. The enumerated names may be passed togetInstance()
.- Returns:
- An
Enumeration
overString
objects - See Also:
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getAvailableSources
Returns an enumeration over the source names of registered transliterators. Source names may be passed to getAvailableTargets() to obtain available targets for each source. -
getAvailableTargets
Returns an enumeration over the target names of registered transliterators having a given source name. Target names may be passed to getAvailableVariants() to obtain available variants for each source and target pair. -
getAvailableVariants
Returns an enumeration over the variant names of registered transliterators having a given source name and target name. -
registerAny
Deprecated.This API is ICU internal only.Register the script-based "Any" transliterators: Any-Latin, Any-Greek -
transform
Implements StringTransform via this method.
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