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:
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:
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:
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());
}
}
}
OutputMatch 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 = "geeksforgeeks";
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());
}
}
OutputCurrent REGEX: geek
Current INPUT: geeksforgeeks
lookingAt(): true
matches(): false