SymbolTable


1   /*
2    *******************************************************************************
3    * Copyright (C) 1996-2005, International Business Machines Corporation and    *
4    * others. All Rights Reserved.                                                *
5    *******************************************************************************
6    */
7   package com.ibm.icu.text;
8   import java.text.ParsePosition  ;
9   
10  /**
11   * An interface that defines both lookup protocol and parsing of
12   * symbolic names.
13   * 
14   * <p>This interface is used by UnicodeSet to resolve $Variable style
15   * references that appear in set patterns.  RBBI and Transliteration
16   * both independently implement this interface.
17   *
18   * <p>A symbol table maintains two kinds of mappings.  The first is
19   * between symbolic names and their values.  For example, if the
20   * variable with the name "start" is set to the value "alpha"
21   * (perhaps, though not necessarily, through an expression such as
22   * "$start=alpha"), then the call lookup("start") will return the
23   * char[] array ['a', 'l', 'p', 'h', 'a'].
24   *
25   * <p>The second kind of mapping is between character values and
26   * UnicodeMatcher objects.  This is used by RuleBasedTransliterator,
27   * which uses characters in the private use area to represent objects
28   * such as UnicodeSets.  If U+E015 is mapped to the UnicodeSet [a-z],
29   * then lookupMatcher(0xE015) will return the UnicodeSet [a-z].
30   *
31   * <p>Finally, a symbol table defines parsing behavior for symbolic
32   * names.  All symbolic names start with the SYMBOL_REF character.
33   * When a parser encounters this character, it calls parseReference()
34   * with the position immediately following the SYMBOL_REF.  The symbol
35   * table parses the name, if there is one, and returns it.
36   *
37   * @stable ICU 2.8
38   */
39  public interface SymbolTable {
40  
41      /**
42       * The character preceding a symbol reference name.
43       * @stable ICU 2.8
44       */
45      static final char SYMBOL_REF = '$';
46  
47      /**
48       * Lookup the characters associated with this string and return it.
49       * Return <tt>null</tt> if no such name exists.  The resultant
50       * array may have length zero.
51       * @param s the symbolic name to lookup
52       * @return a char array containing the name's value, or null if
53       * there is no mapping for s.
54       * @stable ICU 2.8
55       */
56      char[] lookup(String   s);
57  
58      /**
59       * Lookup the UnicodeMatcher associated with the given character, and
60       * return it.  Return <tt>null</tt> if not found.
61       * @param ch a 32-bit code point from 0 to 0x10FFFF inclusive.
62       * @return the UnicodeMatcher object represented by the given
63       * character, or null if there is no mapping for ch.
64       * @stable ICU 2.8
65       */
66      UnicodeMatcher lookupMatcher(int ch);
67  
68      /**
69       * Parse a symbol reference name from the given string, starting
70       * at the given position.  If no valid symbol reference name is
71       * found, return null and leave pos unchanged.  That is, if the
72       * character at pos cannot start a name, or if pos is at or after
73       * text.length(), then return null.  This indicates an isolated
74       * SYMBOL_REF character.
75       * @param text the text to parse for the name
76       * @param pos on entry, the index of the first character to parse.
77       * This is the character following the SYMBOL_REF character.  On
78       * exit, the index after the last parsed character.  If the parse
79       * failed, pos is unchanged on exit.
80       * @param limit the index after the last character to be parsed.
81       * @return the parsed name, or null if there is no valid symbolic
82       * name at the given position.
83       * @stable ICU 2.8
84       */
85      String   parseReference(String   text, ParsePosition   pos, int limit);
86  }
87
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