com.nobigsoftware.dfalex

Class StringMatcher

java.lang.Object

com.nobigsoftware.dfalex.StringMatcher

public class StringMatcher
extends java.lang.Object

This class implements fast matching in a string using DFAs

Substrings matching patterns are discoverd with the findNext(DfaState) and matchAt(DfaState, int) methods, both of which take a DFA start state for the patterns to find.

NOTE that you don't have to pass the same state every time -- different calls with the same matcher can search for different patterns and return different kinds of results.

3 pointers are maintained in the string:

• The LastMatchStart position is the position in the source string of the start of the last successful match, or if no match has been performed yet.
• The LastMatchEnd position is the position in the source string of the end of the last successful match, or 0 of no match has been performed yet
• The SearchLimit is highest position to search. This is initially set to the source string length. No characters at positions >= SearchLimit will be included in matches

Constructor Summary

Constructors

Constructor and Description
StringMatcher(java.lang.String src) Create a new StringMatcher.

Method Summary

Modifier and Type	Method and Description
<MATCHRESULT> MATCHRESULT	findNext(DfaState<MATCHRESULT> state) Find the next non-empty match
java.lang.String	getLastMatch() Get the last successful matching substring, or "" if there isn't one.
int	getLastMatchEnd() Get the end position of the last successful match, or 0 if there isn't one
int	getLastMatchStart() Get the start position of the last successful match, or 0 if there isn't one
<MATCHRESULT> MATCHRESULT	matchAt(DfaState<MATCHRESULT> state, int startPos) Find the longest match starting at a given position.
static <MATCHRESULT> MATCHRESULT	matchWholeString(DfaState<MATCHRESULT> state, java.lang.String str) See if a whole string matches a DFA
void	reset() Resets the matcher to its initial state
void	setPositions(int lastMatchStart, int lastMatchEnd, int searchLimit) Set the LastMatchStart, LastMatchEnd, and SearchLimit positions explicitly.

Methods inherited from class java.lang.Object

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

Constructor Detail

StringMatcher

public StringMatcher(java.lang.String src)

Create a new StringMatcher.

The LastMatchStart and LastMatchEnd positions are initialized to zero

Parameters:

src - the source string to be searched

Method Detail

setPositions

public void setPositions(int lastMatchStart,
                         int lastMatchEnd,
                         int searchLimit)

Set the LastMatchStart, LastMatchEnd, and SearchLimit positions explicitly.

Parameters:

lastMatchStart - the new lastMatchStartPosition

lastMatchEnd - the new lastMatchEnd position

searchLimit - the new searchLimit. This will be limited to the source string length, so you can pass Integer.MAX_VALUE to set it to the string length explicitly.

Throws:

java.lang.IndexOutOfBoundsException - if (lastMatchStart < 0 || lastMatchEnd < lastMatchStart || searchLimit < lastMatchEnd)

reset

public void reset()

Resets the matcher to its initial state

This is equivalent to setPositions(0,0,Integer.MAX_VALUE);

getLastMatchStart

public int getLastMatchStart()

Get the start position of the last successful match, or 0 if there isn't one

Returns:

the current LastMatchStart position

getLastMatchEnd

public int getLastMatchEnd()

Get the end position of the last successful match, or 0 if there isn't one

Returns:

the current LastMatchEnd position

getLastMatch

public java.lang.String getLastMatch()

Get the last successful matching substring, or "" if there isn't one.

Returns:

The last successful matching string or empty.

findNext

public <MATCHRESULT> MATCHRESULT findNext(DfaState<MATCHRESULT> state)

Find the next non-empty match

The string is searched from getLastMatchEnd() to the search limit to find a substring that matches a pattern in the given DFA.

If there is a match, then the LastMatchStart and LastMatchEnd positions are set to the start and end of the first match, and the MATCHRESULT that the DFA produces for that match is returned.

If there is more than one match starting at the same position, the longest one is selected.

Type Parameters:

MATCHRESULT - the type of results produced by the DFA

Parameters:

state - The start state of the DFA for the patterns you want to find

Returns:

The MATCHRESULT for the next non-empty match in the string, or null if there isn't one

matchAt

public <MATCHRESULT> MATCHRESULT matchAt(DfaState<MATCHRESULT> state,
                                         int startPos)

Find the longest match starting at a given position.

If there is a non-empty match for the DFA in the source string starting at startPos, then the LastMatchStart position is set to startPos, the LastMatchEnd position is set to the end of the longest such match, and the MATCHRESULT from that match is returned.

Type Parameters:

MATCHRESULT - the type of results produced by the DFA

Parameters:

state - The start state of the DFA for the patterns you want to match

startPos - the position in the source string to test for a match

Returns:

If the source string matches a pattern in the DFA at startPos, the MATCHRESULT that the pattern match produces. Otherwise null.

matchWholeString

public static <MATCHRESULT> MATCHRESULT matchWholeString(DfaState<MATCHRESULT> state,
                                                         java.lang.String str)

See if a whole string matches a DFA

Type Parameters:

MATCHRESULT - the type of results produced by the DFA

Parameters:

state - DFA start state

str - string to test

Returns:

If the whole string matches the DFA, this is the match result produced. Otherwise null.