Class RE

java.lang.Object
com.codename1.util.regex.RE
public class RE extends Object

RE is an efficient, lightweight regular expression evaluator/matcher class. Regular expressions are pattern descriptions which enable sophisticated matching of strings. In addition to being able to match a string against a pattern, you can also extract parts of the match. This is especially useful in text parsing! Details on the syntax of regular expression patterns are given below.

To compile a regular expression (RE), you can simply construct an RE matcher object from the string specification of the pattern, like this:

 RE r = new RE("a*b");

Once you have done this, you can call either of the RE.match methods to perform matching on a String. For example:

 boolean matched = r.match("aaaab");

will cause the boolean matched to be set to true because the pattern "a*b" matches the string "aaaab".

If you were interested in the number of a's which matched the first part of our example expression, you could change the expression to "(a*)b". Then when you compiled the expression and matched it against something like "xaaaab", you would get results like this:

 RE r = new RE("(a*)b");                  // Compile expression
 boolean matched = r.match("xaaaab");     // Match against "xaaaab"

 String wholeExpr = r.getParen(0);        // wholeExpr will be 'aaaab'
 String insideParens = r.getParen(1);     // insideParens will be 'aaaa'

 int startWholeExpr = r.getParenStart(0); // startWholeExpr will be index 1
 int endWholeExpr = r.getParenEnd(0);     // endWholeExpr will be index 6
 int lenWholeExpr = r.getParenLength(0);  // lenWholeExpr will be 5

 int startInside = r.getParenStart(1);    // startInside will be index 1
 int endInside = r.getParenEnd(1);        // endInside will be index 5
 int lenInside = r.getParenLength(1);     // lenInside will be 4

You can also refer to the contents of a parenthesized expression within a regular expression itself. This is called a 'backreference'. The first backreference in a regular expression is denoted by \1, the second by \2 and so on. So the expression:

 ([0-9]+)=\1

will match any string of the form n=n (like 0=0 or 2=2).

The full regular expression syntax accepted by RE is described here:

 **Characters**

   *unicodeChar*   Matches any identical unicode character
   \                    Used to quote a meta-character (like '*')
   \\                   Matches a single '\' character
   \0nnn                Matches a given octal character
   \xhh                 Matches a given 8-bit hexadecimal character
   \\uhhhh              Matches a given 16-bit hexadecimal character
   \t                   Matches an ASCII tab character
   \n                   Matches an ASCII newline character
   \r                   Matches an ASCII return character
   \f                   Matches an ASCII form feed character

 **Character Classes**

   [abc]                Simple character class
   [a-zA-Z]             Character class with ranges
   [^abc]               Negated character class

NOTE: Incomplete ranges will be interpreted as "starts from zero" or "ends with last character".

I.e. [-a] is the same as [\u0000-a], and [a-] is the same as [a-\uFFFF], [-] means "all characters".

 **Standard POSIX Character Classes**

   [:alnum:]            Alphanumeric characters.
   [:alpha:]            Alphabetic characters.
   [:blank:]            Space and tab characters.
   [:cntrl:]            Control characters.
   [:digit:]            Numeric characters.
   [:graph:]            Characters that are printable and are also visible.
                        (A space is printable, but not visible, while an
                        `a' is both.)
   [:lower:]            Lower-case alphabetic characters.
   [:print:]            Printable characters (characters that are not
                        control characters.)
   [:punct:]            Punctuation characters (characters that are not letter,
                        digits, control characters, or space characters).
   [:space:]            Space characters (such as space, tab, and formfeed,
                        to name a few).
   [:upper:]            Upper-case alphabetic characters.
   [:xdigit:]           Characters that are hexadecimal digits.

 **Non-standard POSIX-style Character Classes**

   [:javastart:]        Start of a Java identifier
   [:javapart:]         Part of a Java identifier

 **Predefined Classes**

   .         Matches any character other than newline
   \w        Matches a "word" character (alphanumeric plus "_")
   \W        Matches a non-word character
   \s        Matches a whitespace character
   \S        Matches a non-whitespace character
   \d        Matches a digit character
   \D        Matches a non-digit character

 **Boundary Matchers**

   ^         Matches only at the beginning of a line
   $         Matches only at the end of a line
   \b        Matches only at a word boundary
   \B        Matches only at a non-word boundary

 **Greedy Closures**

   A*        Matches A 0 or more times (greedy)
   A+        Matches A 1 or more times (greedy)
   A?        Matches A 1 or 0 times (greedy)
   A{n}      Matches A exactly n times (greedy)
   A{n,}     Matches A at least n times (greedy)
   A{n,m}    Matches A at least n but not more than m times (greedy)

 **Reluctant Closures**

   A*?       Matches A 0 or more times (reluctant)
   A+?       Matches A 1 or more times (reluctant)
   A??       Matches A 0 or 1 times (reluctant)

 **Logical Operators**

   AB        Matches A followed by B
   A|B       Matches either A or B
   (A)       Used for subexpression grouping
  (?:A)      Used for subexpression clustering (just like grouping but
             no backrefs)

 **Backreferences**

   \1    Backreference to 1st parenthesized subexpression
   \2    Backreference to 2nd parenthesized subexpression
   \3    Backreference to 3rd parenthesized subexpression
   \4    Backreference to 4th parenthesized subexpression
   \5    Backreference to 5th parenthesized subexpression
   \6    Backreference to 6th parenthesized subexpression
   \7    Backreference to 7th parenthesized subexpression
   \8    Backreference to 8th parenthesized subexpression
   \9    Backreference to 9th parenthesized subexpression

All closure operators (+, *, ?, {m,n}) are greedy by default, meaning that they match as many elements of the string as possible without causing the overall match to fail. If you want a closure to be reluctant (non-greedy), you can simply follow it with a '?'. A reluctant closure will match as few elements of the string as possible when finding matches. {m,n} closures don't currently support reluctancy.

Line terminators

A line terminator is a one- or two-character sequence that marks the end of a line of the input character sequence. The following are recognized as line terminators:

  • A newline (line feed) character ('\n'),

  • A carriage-return character followed immediately by a newline character ("\r\n"),

  • A standalone carriage-return character ('\r'),

  • A next-line character ('…'),

  • A line-separator character ('
'), or

  • A paragraph-separator character ('
).

RE runs programs compiled by the RECompiler class. But the RE matcher class does not include the actual regular expression compiler for reasons of efficiency. You can construct a single RECompiler object and re-use it to compile each expression. Similarly, you can change the program run by a given matcher object at any time. However, RE and RECompiler are not threadsafe (for efficiency reasons, and because requiring thread safety in this class is deemed to be a rare requirement), so you will need to construct a separate compiler or matcher object for each thread (unless you do thread synchronization yourself). Once expression compiled into the REProgram object, REProgram can be safely shared across multiple threads and RE objects.

ISSUES:

  • com.weusours.util.re is not currently compatible with all standard POSIX regcomp flags

  • com.weusours.util.re does not support POSIX equivalence classes ([=foo=] syntax) (I18N/locale issue)

  • com.weusours.util.re does not support nested POSIX character classes (definitely should, but not completely trivial)

  • com.weusours.util.re Does not support POSIX character collation concepts ([.foo.] syntax) (I18N/locale issue)

  • Should there be different matching styles (simple, POSIX, Perl etc?)

  • Should RE support character iterators (for backwards RE matching!)?

  • Should RE support reluctant {m,n} closures (does anyone care)?

  • Not all possibilities are considered for greediness when backreferences are involved (as POSIX suggests should be the case). The POSIX RE "(ac*)c*d

invalid reference 
ac
*\1", when matched against "acdacaa" should yield a match

of acdacaa where \1 is "a". This is not the case in this RE package, and actually Perl doesn't go to this extent either! Until someone actually complains about this, I'm not sure it's worth "fixing". If it ever is fixed, test #137 in RETest.txt should be updated.

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    MATCH_CASEINDEPENDENT
    Flag to indicate that matching should be case-independent (folded)
    static final int
    MATCH_MULTILINE
    Newlines should match as BOL/EOL (^ and $)
    static final int
    MATCH_NORMAL
    Specifies normal, case-sensitive matching behaviour.
    static final int
    MATCH_SINGLELINE
    Consider all input a single body of text - newlines are matched by .
    static final int
    REPLACE_ALL
    Flag bit that indicates that subst should replace all occurrences of this regular expression.
    static final int
    REPLACE_BACKREFERENCES
    Flag bit that indicates that subst should replace backreferences
    static final int
    REPLACE_FIRSTONLY
    Flag bit that indicates that subst should only replace the first occurrence of this regular expression.

  • Constructor Summary

    Constructors
    Constructor
    Description
    RE()
    Constructs a regular expression matcher with no initial program.
    RE(REProgram program)
    Construct a matcher for a pre-compiled regular expression from program (bytecode) data.
    RE(REProgram program, int matchFlags)
    Construct a matcher for a pre-compiled regular expression from program (bytecode) data.
    RE(String pattern)
    Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler.
    RE(String pattern, int matchFlags)
    Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler.

  • Method Summary

    Modifier and Type
    Method
    Description
    int
    getMatchFlags()
    Returns the current match behaviour flags.
    String
    getParen(int which)
    Gets the contents of a parenthesized subexpression after a successful match.
    int
    getParenCount()
    Returns the number of parenthesized subexpressions available after a successful match.
    final int
    getParenEnd(int which)
    Returns the end index of a given paren level.
    final int
    getParenLength(int which)
    Returns the length of a given paren level.
    final int
    getParenStart(int which)
    Returns the start index of a given paren level.
    REProgram
    getProgram()
    Returns the current regular expression program in use by this matcher object.
    String[]
    grep(Object[] search)
    Returns an array of Strings, whose toString representation matches a regular expression.
    protected void
    internalError(String s)
    Throws an Error representing an internal error condition probably resulting from a bug in the regular expression compiler (or possibly data corruption).
    boolean
    match(CharacterIterator search, int i)
    Matches the current regular expression program against a character array, starting at a given index.
    boolean
    match(String search)
    Matches the current regular expression program against a String.
    boolean
    match(String search, int i)
    Matches the current regular expression program against a character array, starting at a given index.
    protected boolean
    matchAt(int i)
    Match the current regular expression program against the current input string, starting at index i of the input string.
    protected int
    matchNodes(int firstNode, int lastNode, int idxStart)
    Try to match a string against a subset of nodes in the program
    void
    setMatchFlags(int matchFlags)
    Sets match behaviour flags which alter the way RE does matching.
    protected final void
    setParenEnd(int which, int i)
    Sets the end of a paren level
    protected final void
    setParenStart(int which, int i)
    Sets the start of a paren level
    void
    setProgram(REProgram program)
    Sets the current regular expression program used by this matcher object.
    static String
    simplePatternToFullRegularExpression(String pattern)
    Converts a 'simplified' regular expression to a full regular expression
    String[]
    split(String s)
    Splits a string into an array of strings on regular expression boundaries.
    String
    subst(String substituteIn, String substitution)
    Substitutes a string for this regular expression in another string.
    String
    subst(String substituteIn, String substitution, int flags)
    Substitutes a string for this regular expression in another string.

    Methods inherited from class Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

  • Field Details

    • MATCH_NORMAL

      public static final int MATCH_NORMAL
      Specifies normal, case-sensitive matching behaviour.
      See Also:

    • MATCH_CASEINDEPENDENT

      public static final int MATCH_CASEINDEPENDENT
      Flag to indicate that matching should be case-independent (folded)
      See Also:

    • MATCH_MULTILINE

      public static final int MATCH_MULTILINE
      Newlines should match as BOL/EOL (^ and $)
      See Also:

    • MATCH_SINGLELINE

      public static final int MATCH_SINGLELINE
      Consider all input a single body of text - newlines are matched by .
      See Also:

    • REPLACE_ALL

      public static final int REPLACE_ALL
      Flag bit that indicates that subst should replace all occurrences of this regular expression.
      See Also:

    • REPLACE_FIRSTONLY

      public static final int REPLACE_FIRSTONLY
      Flag bit that indicates that subst should only replace the first occurrence of this regular expression.
      See Also:

    • REPLACE_BACKREFERENCES

      public static final int REPLACE_BACKREFERENCES
      Flag bit that indicates that subst should replace backreferences
      See Also:

  • Constructor Details

    • RE

      public RE(String pattern) throws RESyntaxException

      Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler. If you will be compiling many expressions, you may prefer to use a single RECompiler object instead.

      Parameters
      • pattern: The regular expression pattern to compile.
      Throws
      • RESyntaxException: Thrown if the regular expression has invalid syntax.
      See also
      • RECompiler
      Throws:
      RESyntaxException

    • RE

      public RE(String pattern, int matchFlags) throws RESyntaxException

      Constructs a regular expression matcher from a String by compiling it using a new instance of RECompiler. If you will be compiling many expressions, you may prefer to use a single RECompiler object instead.

      Parameters

      • pattern: The regular expression pattern to compile.

      • matchFlags: The matching style

      Throws
      • RESyntaxException: Thrown if the regular expression has invalid syntax.
      See also
      • RECompiler
      Throws:
      RESyntaxException

    • RE

      public RE(REProgram program, int matchFlags)

      Construct a matcher for a pre-compiled regular expression from program (bytecode) data. Permits special flags to be passed in to modify matching behaviour.

      Parameters

      • program: Compiled regular expression program (see RECompiler)

      • matchFlags: @param matchFlags One or more of the RE match behaviour flags (RE.MATCH_*):

                                            MATCH_NORMAL              // Normal (case-sensitive) matching
                                      MATCH_CASEINDEPENDENT     // Case folded comparisons
                                      MATCH_MULTILINE           // Newline matches as BOL/EOL
      See also

      • RECompiler

      • REProgram

    • RE

      public RE(REProgram program)

      Construct a matcher for a pre-compiled regular expression from program (bytecode) data.

      Parameters
      • program: Compiled regular expression program
      See also
      • RECompiler

    • RE

      public RE()
      Constructs a regular expression matcher with no initial program. This is likely to be an uncommon practice, but is still supported.

  • Method Details

    • simplePatternToFullRegularExpression

      public static String simplePatternToFullRegularExpression(String pattern)

      Converts a 'simplified' regular expression to a full regular expression

      Parameters
      • pattern: The pattern to convert
      Returns

      The full regular expression

    • getMatchFlags

      public int getMatchFlags()

      Returns the current match behaviour flags.

      Returns
      Returns:

      Current match behaviour flags (RE.MATCH_*).

        MATCH_NORMAL              // Normal (case-sensitive) matching
  MATCH_CASEINDEPENDENT     // Case folded comparisons
  MATCH_MULTILINE           // Newline matches as BOL/EOL
      See also
      • #setMatchFlags

    • setMatchFlags

      public void setMatchFlags(int matchFlags)

      Sets match behaviour flags which alter the way RE does matching.

      Parameters
      • matchFlags: @param matchFlags One or more of the RE match behaviour flags (RE.MATCH_*):
                                            MATCH_NORMAL              // Normal (case-sensitive) matching
                                      MATCH_CASEINDEPENDENT     // Case folded comparisons
                                      MATCH_MULTILINE           // Newline matches as BOL/EOL

    • getProgram

      public REProgram getProgram()

      Returns the current regular expression program in use by this matcher object.

      Returns

      Regular expression program

      See also
      • #setProgram

    • setProgram

      public void setProgram(REProgram program)

      Sets the current regular expression program used by this matcher object.

      Parameters
      • program: Regular expression program compiled by RECompiler.
      See also

      • RECompiler

      • REProgram

    • getParenCount

      public int getParenCount()

      Returns the number of parenthesized subexpressions available after a successful match.

      Returns

      Number of available parenthesized subexpressions

    • getParen

      public String getParen(int which)

      Gets the contents of a parenthesized subexpression after a successful match.

      Parameters
      • which: Nesting level of subexpression
      Returns

      String

    • getParenStart

      public final int getParenStart(int which)

      Returns the start index of a given paren level.

      Parameters
      • which: Nesting level of subexpression
      Returns

      String index

    • getParenEnd

      public final int getParenEnd(int which)

      Returns the end index of a given paren level.

      Parameters
      • which: Nesting level of subexpression
      Returns

      String index

    • getParenLength

      public final int getParenLength(int which)

      Returns the length of a given paren level.

      Parameters
      • which: Nesting level of subexpression
      Returns

      Number of characters in the parenthesized subexpression

    • setParenStart

      protected final void setParenStart(int which, int i)

      Sets the start of a paren level

      Parameters

      • which: Which paren level

      • i: Index in input array

    • setParenEnd

      protected final void setParenEnd(int which, int i)

      Sets the end of a paren level

      Parameters

      • which: Which paren level

      • i: Index in input array

    • internalError

      protected void internalError(String s) throws Error

      Throws an Error representing an internal error condition probably resulting from a bug in the regular expression compiler (or possibly data corruption). In practice, this should be very rare.

      Parameters
      • s: Error description
      Throws:
      Error

    • matchNodes

      protected int matchNodes(int firstNode, int lastNode, int idxStart)

      Try to match a string against a subset of nodes in the program

      Parameters

      • firstNode: Node to start at in program

      • lastNode: @param lastNode Last valid node (used for matching a subexpression without matching the rest of the program as well).

      • idxStart: Starting position in character array

      Returns

      Final input array index if match succeeded. -1 if not.

    • matchAt

      protected boolean matchAt(int i)

      Match the current regular expression program against the current input string, starting at index i of the input string. This method is only meant for internal use.

      Parameters
      • i: The input string index to start matching at
      Returns

      True if the input matched the expression

    • match

      public boolean match(String search, int i)

      Matches the current regular expression program against a character array, starting at a given index.

      Parameters

      • search: String to match against

      • i: Index to start searching at

      Returns

      True if string matched

    • match

      public boolean match(CharacterIterator search, int i)

      Matches the current regular expression program against a character array, starting at a given index.

      Parameters

      • search: String to match against

      • i: Index to start searching at

      Returns

      True if string matched

    • match

      public boolean match(String search)

      Matches the current regular expression program against a String.

      Parameters
      • search: String to match against
      Returns

      True if string matched

    • split

      public String[] split(String s)

      Splits a string into an array of strings on regular expression boundaries. This function works the same way as the Perl function of the same name. Given a regular expression of "

      invalid reference 
      ab
      +" and a string to split of

      "xyzzyababbayyzabbbab123", the result would be the array of Strings "[xyzzy, yyz, 123]".

      Please note that the first string in the resulting array may be an empty string. This happens when the very first character of input string is matched by the pattern.

      Parameters
      • s: String to split on this regular exression
      Returns

      Array of strings

    • subst

      public String subst(String substituteIn, String substitution)

      Substitutes a string for this regular expression in another string. This method works like the Perl function of the same name. Given a regular expression of "a*b", a String to substituteIn of "aaaabfooaaabgarplyaaabwackyb" and the substitution String "-", the resulting String returned by subst would be "-foo-garply-wacky-".

      Parameters

      • substituteIn: String to substitute within

      • substitution: String to substitute for all matches of this regular expression.

      Returns
      Returns:
      The string substituteIn with zero or more occurrences of the current regular expression replaced with the substitution String (if this regular expression object doesn't match at any position, the original String is returned unchanged).

    • subst

      public String subst(String substituteIn, String substitution, int flags)

      Substitutes a string for this regular expression in another string. This method works like the Perl function of the same name. Given a regular expression of "a*b", a String to substituteIn of "aaaabfooaaabgarplyaaabwackyb" and the substitution String "-", the resulting String returned by subst would be "-foo-garply-wacky-".

      It is also possible to reference the contents of a parenthesized expression with $0, $1, ... $9. A regular expression of "http://[\.\w\-\?/~_@&=%]+", a String to substituteIn of "visit us: http://www.apache.org!" and the substitution String "<a href="$0">$0", the resulting String returned by subst would be "visit us: <a href="http://www.apache.org">http://www.apache.org!".

      Note: $0 represents the whole match.

      Parameters

      • substituteIn: String to substitute within

      • substitution: String to substitute for matches of this regular expression

      • flags: @param flags One or more bitwise flags from REPLACE_*. If the REPLACE_FIRSTONLY flag bit is set, only the first occurrence of this regular expression is replaced. If the bit is not set (REPLACE_ALL), all occurrences of this pattern will be replaced. If the flag REPLACE_BACKREFERENCES is set, all backreferences will be processed.

      Returns
      Returns:
      The string substituteIn with zero or more occurrences of the current regular expression replaced with the substitution String (if this regular expression object doesn't match at any position, the original String is returned unchanged).

    • grep

      public String[] grep(Object[] search)

      Returns an array of Strings, whose toString representation matches a regular expression. This method works like the Perl function of the same name. Given a regular expression of "a*b" and an array of String objects of [foo, aab, zzz, aaaab], the array of Strings returned by grep would be [aab, aaaab].

      Parameters
      • search: Array of Objects to search
      Returns

      Array of Strings whose toString() value matches this regular expression.