Package it.unimi.dsi.util

Class TextPattern

java.lang.Object
it.unimi.dsi.util.TextPattern
All Implemented Interfaces:
Serializable, CharSequence
public class TextPattern
extends Object
implements Serializable, CharSequence
QuickSearch matching against a constant string.

The regular expression facilities of the Java API are a powerful tool; however, when searching for a constant pattern many algorithms can increase of orders magnitude the speed of a search.

This class provides constant-pattern text search facilities by implementing Sunday's QuickSearch (a simplified but very effective variant of the Boyer—Moore search algorithm) using compact approximators, a randomised data structure that can accomodate in a small space (but in an approximated way) the bad-character shift table of a large alphabet such as Unicode.

Since a large subset of US-ASCII is used in all languages (e.g., whitespace, punctuation, etc.), this class caches separately the shifts for the first 128 Unicode characters, resulting in very good performance even on text in pure US-ASCII.

Note that the indexOf methods of MutableString use a even more simplified variant of QuickSearch which is less efficient, but has a smaller setup time and does not generate any object. The search facilities provided by this class are targeted at searches on very large texts, repeated searches with the same pattern, and case-insensitive searches.

Instances of this class are immutable and thread-safe.

This class is experimental: APIs could change with the next release.

Since:
0.6
Author:
Sebastiano Vigna, Paolo Boldi
See Also:
Serialized Form

  • Field Summary

    Fields 
    Modifier and Type Field Description
    static int CASE_INSENSITIVE
    Enables case-insensitive matching.
    protected char[] pattern
    The pattern backing array.
    static int UNICODE_CASE
    Enables Unicode-aware case folding.

  • Constructor Summary

    Constructors 
    Constructor Description
    TextPattern​(CharSequence pattern)
    Creates a new case-sensitive TextPattern object that can be used to search for the given pattern.
    TextPattern​(CharSequence pattern, int flags)
    Creates a new TextPattern object that can be used to search for the given pattern.

  • Method Summary

    Modifier and Type Method Description
    boolean caseInsensitive()
    Returns whether this pattern is case insensitive.
    char charAt​(int i)  
    boolean equals​(Object o)
    Compares this text pattern to another object.
    int hashCode()
    Returns a hash code for this text pattern.
    int length()  
    int search​(byte[] a)
    Returns the index of the first occurrence of this pattern in the given byte array.
    int search​(byte[] a, int from)
    Returns the index of the first occurrence of this pattern in the given byte array starting from a given index.
    int search​(byte[] a, int from, int to)
    Returns the index of the first occurrence of this pattern in the given byte array between given indices.
    int search​(char[] array)
    Returns the index of the first occurrence of this pattern in the given character array.
    int search​(char[] array, int from)
    Returns the index of the first occurrence of this pattern in the given character array starting from a given index.
    int search​(char[] a, int from, int to)
    Returns the index of the first occurrence of this pattern in the given character array between given indices.
    int search​(CharList list)
    Returns the index of the first occurrence of this pattern in the given character list.
    int search​(CharList list, int from)
    Returns the index of the first occurrence of this pattern in the given character list starting from a given index.
    int search​(CharList list, int from, int to)
    Returns the index of the first occurrence of this pattern in the given character list between given indices.
    int search​(CharSequence s)
    Returns the index of the first occurrence of this pattern in the given character sequence.
    int search​(CharSequence s, int from)
    Returns the index of the first occurrence of this pattern in the given character sequence starting from a given index.
    int search​(CharSequence s, int from, int to)
    Returns the index of the first occurrence of this pattern in the given character sequence between given indices.
    CharSequence subSequence​(int from, int to)  
    String toString()  
    boolean unicodeCase()
    Returns whether this pattern uses Unicode case folding.

    Methods inherited from class java.lang.Object

    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

    Methods inherited from interface java.lang.CharSequence

    chars, codePoints

  • Field Details

    • CASE_INSENSITIVE

      public static final int CASE_INSENSITIVE
      Enables case-insensitive matching.

      By default, case-insensitive matching assumes that only characters in the ASCII charset are being matched. Unicode-aware case-insensitive matching can be enabled by specifying the UNICODE_CASE flag in conjunction with this flag.

      Case-insensitivity involves a performance drop.

      See Also:
      Constant Field Values

    • UNICODE_CASE

      public static final int UNICODE_CASE
      Enables Unicode-aware case folding.

      When this flag is specified then case-insensitive matching, when enabled by the CASE_INSENSITIVE flag, is done in a manner consistent with the Unicode Standard. By default, case-insensitive matching assumes that only characters in the ASCII charset are being matched.

      Unicode-aware case folding is very expensive (two method calls per examined non-ASCII character).

      See Also:
      Constant Field Values

    • pattern

      protected char[] pattern
      The pattern backing array.

  • Constructor Details

    • TextPattern

      public TextPattern​(CharSequence pattern)
      Creates a new case-sensitive TextPattern object that can be used to search for the given pattern.
      Parameters:
      pattern - the constant pattern to search for.

    • TextPattern

      public TextPattern​(CharSequence pattern, int flags)
      Creates a new TextPattern object that can be used to search for the given pattern.
      Parameters:
      pattern - the constant pattern to search for.
      flags - a bit mask that may include CASE_INSENSITIVE and UNICODE_CASE.

  • Method Details

    • caseInsensitive

      public boolean caseInsensitive()
      Returns whether this pattern is case insensitive.

    • unicodeCase

      public boolean unicodeCase()
      Returns whether this pattern uses Unicode case folding.

    • length

      public int length()
      Specified by:
      length in interface CharSequence

    • charAt

      public char charAt​(int i)
      Specified by:
      charAt in interface CharSequence

    • subSequence

      public CharSequence subSequence​(int from, int to)
      Specified by:
      subSequence in interface CharSequence

    • search

      public int search​(char[] array)
      Returns the index of the first occurrence of this pattern in the given character array.
      Parameters:
      array - the character array to look in.
      Returns:
      the index of the first occurrence of this pattern contained in the given array, or -1, if the pattern cannot be found.

    • search

      public int search​(char[] array, int from)
      Returns the index of the first occurrence of this pattern in the given character array starting from a given index.
      Parameters:
      array - the character array to look in.
      from - the index from which the search must start.
      Returns:
      the index of the first occurrence of this pattern contained in the subarray starting from from (inclusive), or -1, if the pattern cannot be found.

    • search

      public int search​(char[] a, int from, int to)
      Returns the index of the first occurrence of this pattern in the given character array between given indices.
      Parameters:
      a - the character array to look in.
      from - the index from which the search must start.
      to - the index at which the search must end.
      Returns:
      the index of the first occurrence of this pattern contained in the subarray starting from from (inclusive) up to to (exclusive) characters, or -1, if the pattern cannot be found.

    • search

      public int search​(CharSequence s)
      Returns the index of the first occurrence of this pattern in the given character sequence.
      Parameters:
      s - the character sequence to look in.
      Returns:
      the index of the first occurrence of this pattern contained in the given character sequence, or -1, if the pattern cannot be found.

    • search

      public int search​(CharSequence s, int from)
      Returns the index of the first occurrence of this pattern in the given character sequence starting from a given index.
      Parameters:
      s - the character array to look in.
      from - the index from which the search must start.
      Returns:
      the index of the first occurrence of this pattern contained in the subsequence starting from from (inclusive), or -1, if the pattern cannot be found.

    • search

      public int search​(CharSequence s, int from, int to)
      Returns the index of the first occurrence of this pattern in the given character sequence between given indices.
      Parameters:
      s - the character array to look in.
      from - the index from which the search must start.
      to - the index at which the search must end.
      Returns:
      the index of the first occurrence of this pattern contained in the subsequence starting from from (inclusive) up to to (exclusive) characters, or -1, if the pattern cannot be found.

    • search

      public int search​(byte[] a)
      Returns the index of the first occurrence of this pattern in the given byte array.
      Parameters:
      a - the byte array to look in.
      Returns:
      the index of the first occurrence of this pattern contained in the given byte array, or -1, if the pattern cannot be found.

    • search

      public int search​(byte[] a, int from)
      Returns the index of the first occurrence of this pattern in the given byte array starting from a given index.
      Parameters:
      a - the byte array to look in.
      from - the index from which the search must start.
      Returns:
      the index of the first occurrence of this pattern contained in the array fragment starting from from (inclusive), or -1, if the pattern cannot be found.

    • search

      public int search​(byte[] a, int from, int to)
      Returns the index of the first occurrence of this pattern in the given byte array between given indices.
      Parameters:
      a - the byte array to look in.
      from - the index from which the search must start.
      to - the index at which the search must end.
      Returns:
      the index of the first occurrence of this pattern contained in the array fragment starting from from (inclusive) up to to (exclusive) characters, or -1, if the pattern cannot be found. TODO: this must be tested

    • search

      public int search​(CharList list)
      Returns the index of the first occurrence of this pattern in the given character list.
      Parameters:
      list - the character list to look in.
      Returns:
      the index of the first occurrence of this pattern contained in the given list, or -1, if the pattern cannot be found.

    • search

      public int search​(CharList list, int from)
      Returns the index of the first occurrence of this pattern in the given character list starting from a given index.
      Parameters:
      list - the character list to look in.
      from - the index from which the search must start.
      Returns:
      the index of the first occurrence of this pattern contained in the sublist starting from from (inclusive), or -1, if the pattern cannot be found.

    • search

      public int search​(CharList list, int from, int to)
      Returns the index of the first occurrence of this pattern in the given character list between given indices.
      Parameters:
      list - the character list to look in.
      from - the index from which the search must start.
      to - the index at which the search must end.
      Returns:
      the index of the first occurrence of this pattern contained in the sublist starting from from (inclusive) up to to (exclusive) characters, or -1, if the pattern cannot be found.

    • equals

      public final boolean equals​(Object o)
      Compares this text pattern to another object.

      This method will return true iff its argument is a TextPattern containing the same constant pattern with the same flags set.

      Overrides:
      equals in class Object
      Parameters:
      o - an object.
      Returns:
      true if the argument is a TextPatterns that contains the same constant pattern of this text pattern and has the same flags set.

    • hashCode

      public final int hashCode()
      Returns a hash code for this text pattern.

      The hash code of a text pattern is the same as that of a String with the same content (suitably lower cased, if the pattern is case insensitive).

      Overrides:
      hashCode in class Object
      Returns:
      a hash code array for this object.
      See Also:
      String.hashCode()

    • toString

      public final String toString()
      Specified by:
      toString in interface CharSequence
      Overrides:
      toString in class Object