Java Matcher example

Java Matcher example

Here is an example of using the Java Matcher class to perform pattern matching on a given input string:

import java.util.regex.Matcher;
import java.util.regex.Pattern;
public class Main {
public static void main(String[] args) {
// Create a Pattern object
String regex = "Hello (w+), (d+)!";  // Define the regular expression pattern
Pattern p = Pattern.compile(regex);
// Create a Matcher object
String input = "Hello John, 23!";
Matcher m = p.matcher(input);  // Pass the input string to the matcher
if(m.matches()) {
System.out.println("Matched!");
int count = 0;
while (m.find()) { // Find all occurrences of the pattern
System.out.println("Found: " + m.group());
count++;
}
System.out.println("Total matches found: " + count);
} else {
System.out.println("Not matched!");
}
}
}

In this example, we are using the java.util.regex package to create a regular expression pattern that matches the string "Hello", followed by one or more word characters (captured in group 1), followed by a comma, followed by one or more digits (captured in group 2), and finally followed by an exclamation mark.

We then pass this input string to the Pattern.compile() method to create a Pattern object. This Pattern object can be used to create a Matcher object using the matcher() method.

The Matcher object provides several methods for finding matches of the pattern in the input string:

In this example, we use the matches() method to check if the entire input string matches the pattern. If it does, we then use the find() method to find all occurrences of the pattern and print out each match using the group() method.

This is a basic demonstration of how you can use the Java Matcher class to perform pattern matching on input strings.

Java matcher group index

I'd be happy to explain the concept of a "group index" in Java regular expressions using English only.

In Java regular expressions, a "group index" refers to the numerical identifier assigned to each capture group within the pattern. A capture group is a part of the pattern enclosed by parentheses (( and )) that allows you to match and remember a specific part of the input string.

When you create a regular expression with multiple capture groups, Java assigns a unique index to each group starting from 1. The group indices are used to reference the matched groups in the subsequent code, such as extracting the captured text or using it for further processing.

Here's an example to illustrate this:

Pattern pattern = Pattern.compile("(w+)-(d+)");
String input = "hello-123";
Matcher matcher = pattern.matcher(input);
if (matcher.matches()) {
int group1Index = matcher.group(1);
int group2Index = matcher.group(2);
System.out.println("Group 1: " + matcher.group(group1Index));
System.out.println("Group 2: " + matcher.group(group2Index));
}

In this example, the regular expression (w+)-(d+) has two capture groups: one for matching word characters (w+) and another for matching digits (d+). The parentheses around these patterns create capture groups.

When we call matcher.matches() to check if the input string "hello-123" matches the pattern, Java assigns a unique index to each capture group. In this case, the first capture group (word characters) gets an index of 1, and the second capture group (digits) gets an index of 2.

To access the matched text for each group, we use matcher.group(index) where index is the group index. For example, matcher.group(1) returns the matched word characters "hello", and matcher.group(2) returns the matched digits "123".

In summary, a "group index" in Java regular expressions refers to the unique numerical identifier assigned to each capture group within the pattern. These indices are used to reference the matched groups in subsequent code for extraction or further processing.