Regular Expression Syntax:

Here is the table listing down all the regular expression metacharacter syntax available in Java:

SUBEXPRESSION	MATCHES
^	Matches beginning of line.
$	Matches end of line.
.	Matches any single character except newline. Using m option allows it to match newline as well.
[…]	Matches any single character in brackets.
[^…]	Matches any single character not in brackets
\A	Beginning of entire string
\z	End of entire string
\Z	End of entire string except allowable final line terminator.
re*	Matches 0 or more occurrences of preceding expression.
re+	Matches 1 or more of the previous thing
re?	Matches 0 or 1 occurrence of preceding expression.
re{ n}	Matches exactly n number of occurrences of preceding expression.
re{ n,}	Matches n or more occurrences of preceding expression.
re{ n, m}	Matches at least n and at most m occurrences of preceding expression.
a\| b	Matches either a or b.
(re)	Groups regular expressions and remembers matched text.
(?: re)	Groups regular expressions without remembering matched text.
(?> re)	Matches independent pattern without backtracking.
\w	Matches word characters.
\W	Matches nonword characters.
\s	Matches whitespace. Equivalent to [\t\n\r\f].
\S	Matches nonwhitespace.
\d	Matches digits. Equivalent to [0-9].
\D	Matches nondigits.
\A	Matches beginning of string.
\Z	Matches end of string. If a newline exists, it matches just before newline.
\z	Matches end of string.
\G	Matches point where last match finished.
\n	Back-reference to capture group number “n”
\b	Matches word boundaries when outside brackets. Matches backspace (0x08) when inside brackets.
\B	Matches nonword boundaries.
\n, \t, etc.	Matches newlines, carriage returns, tabs, etc.
\Q	Escape (quote) all characters up to \E
\E	Ends quoting begun with \Q

Methods of the Matcher Class:

Here is the lists of useful instance methods:

Index Methods:

Index methods provide useful index values that show precisely where the match was found in the input string:

SN	METHODS WITH DESCRIPTION
1	public int start() Returns the start index of the previous match.
2	public int start(int group) Returns the start index of the subsequence captured by the given group during the previous match operation.
3	public int end() Returns the offset after the last character matched.
4	public int end(int group) Returns the offset after the last character of the subsequence captured by the given group during the previous match operation.

Study Methods:

Study methods review the input string and return a boolean indicating whether or not the pattern is found:

SN	METHODS WITH DESCRIPTION
1	public boolean lookingAt() Attempts to match the input sequence, starting at the beginning of the region, against the pattern.
2	public boolean find() Attempts to find the next subsequence of the input sequence that matches the pattern.
3	public boolean find(int start Resets this matcher and then attempts to find the next subsequence of the input sequence that matches the pattern, starting at the specified index.
4	public boolean matches() Attempts to match the entire region against the pattern.

Replacement Methods:

Replacement methods are useful methods for replacing text in an input string:

SN	METHODS WITH DESCRIPTION
1	public Matcher appendReplacement(StringBuffer sb, String replacement) Implements a non-terminal append-and-replace step.
2	public StringBuffer appendTail(StringBuffer sb) Implements a terminal append-and-replace step.
3	public String replaceAll(String replacement) Replaces every subsequence of the input sequence that matches the pattern with the given replacement string.
4	public String replaceFirst(String replacement) Replaces the first subsequence of the input sequence that matches the pattern with the given replacement string.
5	public static String quoteReplacement(String s) Returns a literal replacement String for the specified String. This method produces a String that will work as a literal replacement s in the appendReplacement method of the Matcher class.

Java Regex

Using the `start` and `end` Methods

Here’s an example, MatcherDemo.java, that counts the number of times the word “dog” appears in the input string.

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class MatcherDemo {

    private static final String REGEX =
        "\\bdog\\b";
    private static final String INPUT =
        "dog dog dog doggie dogg";

    public static void main(String[] args) {
       Pattern p = Pattern.compile(REGEX);
       //  get a matcher object
       Matcher m = p.matcher(INPUT);
       int count = 0;
       while(m.find()) {
           count++;
           System.out.println("Match number "
                              + count);
           System.out.println("start(): "
                              + m.start());
           System.out.println("end(): "
                              + m.end());
      }
   }
}

http://docs.oracle.com/javase/tutorial/essential/regex/matcher.html

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