In Java, Matcher is a class that is implemented by the MatchResult interface, that performs match operations on a character sequence by interpreting a Pattern.
Below, we can see the declaration of java.util.regex.Matcher in java.lang.Object Class:
public final class Matcher extends Object implements MatchResult
By invoking the pattern’s matcher method, a matcher is created from a pattern. If a matcher is created once, we can perform three different kinds of match operations on it:
- matches(): Try to match the total input sequence against the pattern.
- lookingAt(): Try to match the input sequence, against the pattern, starting at the beginning.
- find(): This scans the input sequence and looks for the next subsequence especially matches the pattern.
Methods of Matcher class:
Below the methods of the Matcher class are grouped in the table for convenience according to their functionality.
1. Index Methods:Â
It provides useful index values. It shows precisely whether the match was found in the input string or not:
| S. No. | Method Name | Description |
|---|---|---|
| 1 | public int start() | This method returns the start index of the previous match. |
| 2 | public int start(int group) | This method returns the start index of the subsequence captured by the given group during the previous match operation. |
| 3 | public int end() | This method returns the offset after the last character is matched. |
| 4 | public int end(int group) | This method returns the offset after the last character of the subsequence captured by the given group during the previous match operation. |
2. Study Methods:Â
It reviews the input string and returns a boolean indicating whether the pattern is found or not:
| S. No. | Method Name | Description |
|---|---|---|
| 1 | public boolean lookingAt() | This method aims to match the input sequence, starting at the beginning of the region, against the pattern. |
| 2 | public boolean find() | This method aims to find the next subsequence of the input sequence that matches the pattern. |
| 3 | public boolean find(int start) | Resets this matcher and then tries to find the next subsequence of the input sequence which matches the pattern, starting at the specified index. |
| 4 | public boolean matches() | This method aims to match the entire region against the pattern. |
3. Replacement Methods:Â
These are useful methods for replacing text in an input string:
| S. No. | Method Name | Description |
|---|---|---|
| 1 | public Matcher appendReplacement(StringBuffer sb, String replacement) | This method implements a non-terminal append-and-replace step. |
| 2 | public StringBuffer appendTail(StringBuffer sb) | This method implements a terminal append-and-replace step. |
| 3 | public String replaceAll(String replacement) | This method replaces every subsequence of the input sequence that matches the pattern with the given replacement string. |
| 4 | public String replaceFirst(String replacement) | This method replaces the first subsequence of the input sequence that matches the pattern with the given replacement string. |
| 5 | public static String quoteReplacement(String s) | This method returns a literal replacement String for the specified String, this method also produces a String which will work in the appendReplacement method as a literal replacement of the Matcher class. |
Example 1: Here we can see the example GFG.java which count the number of times the word “geek” appears in the input string using start()  and end() :
Java
// Java program to demonstrate the// methods of Matcher class in Java  import java.util.regex.Matcher;import java.util.regex.Pattern;  public class GFG {      private static final String REGEX = "\\bgeek\\b";    private static final String INPUT        = "geek geek geek geekie geeks";      public static void main(String[] args)    {        Pattern pat = Pattern.compile(REGEX);                // here get a matcher object        Matcher mat = pat.matcher(INPUT);                // initialize a count variable to count        int count = 0;          // try to match the entire input sequence against        // the pattern using the loop        while (mat.find()) {            count++;            System.out.println("Match number " + count);            System.out.println("start(): " + mat.start());            System.out.println("end(): " + mat.end());        }    }} |
Output
Match number 1 start(): 0 end(): 4 Match number 2 start(): 5 end(): 9 Match number 3 start(): 10 end(): 14
Example 2: In this example, we can see GFG.java, the lookingAt() and matches() both attempt to match an input sequence against a pattern.
Java
// Java program to demonstrate the// methods of Matcher class in Java  import java.util.regex.Matcher;import java.util.regex.Pattern;  public class GFG {      private static final String REGEX = "geek";    private static final String INPUT = "neveropen";    private static Pattern pat;    private static Matcher mat;      public static void main(String[] args)    {          // Initialization for pattern and matcher        pat = Pattern.compile(REGEX);        mat = pat.matcher(INPUT);          System.out.println("Current REGEX: " + REGEX);        System.out.println("Current INPUT: " + INPUT);          System.out.println("lookingAt(): "                           + mat.lookingAt());        System.out.println("matches(): " + mat.matches());    }} |
Output
Current REGEX: geek Current INPUT: neveropen lookingAt(): true matches(): false
