https://www.tutorialspoint.com/javaregex/javaregex_capturing_groups.htm

ExampleLive Demoimport java.util.regex.Matcher; import java.util.regex.Pattern; public class NoRegTest {    public static void main(String[] args) {       String s="^fun";       Pattern pattern = Pattern.compile(s);       Matcher matcher = pattern.matcher("Java is fun");       if(!matcher.find()) {          System.out.println("not found");       }    } }Outputnot found

In this program, we will use a regular expression to check if a given string does not contain the substring "kk" using Java. The regular expression ^((?!kk).)*$ is designed to match strings that do not include the "kk" pattern anywhere in the string. The program will evaluate a sample string and print whether or not it contains "kk". Problem Statement Write a program in Java for checking whether a given string contains the substring "kk." If the string does not contain "kk" the program will return true otherwise it will return false. Input String s = "tutorials" Output true ... Read More

In this program, we will use a regular expression to check if a given string does not contain the substring "kk" using Java. The regular expression ^((?!kk).)*$ is designed to match strings that do not include the "kk" pattern anywhere in the string. The program will evaluate a sample string and print whether or not it contains "kk". Problem Statement Write a program in Java for checking whether a given string contains the substring "kk." If the string does not contain "kk" the program will return true otherwise it will return false. Input String s = "tutorials" Output true ... Read More

Exampleimport java.util.regex.*; class PatternMatch{    public static void main(String args[]) {       String content = "I am a student";       String string = ".*boy.*";       boolean isMatch = Pattern.matches(string, content);       System.out.println("The line contains 'boy'?"+ isMatch);    } }Outputthe line contains 'boy'?falsematches()­­It is used to check if the whole text matches a pattern. Its output is boolean. It returns true if match is found otherwise false.This is one of simplest and easiest way of searching a String in a text using Regex .There is a another method compile() , if you want ... Read More

\R matches any line break as defined by the Unicode standardPattern p = Pattern.compile("\R");Unicode line-break sequence is equivalent to \u000D\u000A|[\u000A\u000B\u000C\u000D\u0085\u2028\u2029]

In Java regex matches() matches the input string against the whole string as it add a ^ and $ at the end of the input string.so it will not match the substring. So for matching substring, you should use find().Exampleimport java.util.regex.*; class PatternMatchingExample {    public static void main(String args[]) {       String content = "aabbcc";       String string = "aa";       Pattern p = Pattern.compile(string);       Matcher m = p.matcher(content);       System.out.println(" 'aa' Match:"+ m.matches());       System.out.println(" 'aa' Match:"+ m.find());    } }Output'aa' Match:false 'aa' Match:true

ExampleLive Demoimport java.util.ArrayList; import java.util.List; import java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class SearchRegex {    private Pattern subPattern = Pattern.compile(SUBJECT_PATTERN);    private Matcher matcher;    private static final String SUBJECT_PATTERN = "(?s)Subject 1:\s(.*)Subject 2:";    public static void main(String[] args) {       String d = "Subject 1: Java" + "Subject 2: Python";       SearchRegex obj = new SearchRegex();       List list = obj.getSubject(d);       System.out.println("Address Result : " + list);    }    private List getSubject(String d){       List result = new ArrayList();       matcher = subPattern.matcher(d);       while (matcher.find()) {          result.add(matcher.group(1));       }       return result;    } }OutputAddress Result : [Java]

the syntax? i:x makes the string search case-insensitive. for egpublic class RegCaseSense {    public static void main(String[] args) {       String stringSearch = "HI we are at java class.";       // this won't work because the pattern is in upper-case       System.out.println("Try this 1: " + stringSearch.matches(".*CLASS.*"));         // the magic (?i:X) syntax makes this search case-insensitive, so it returns true       System.out.println("Try this 2: " + stringSearch.matches("(?i:.*CLASS.*)"));    } }

the syntax? i:x makes the string search case-insensitive. for egpublic class RegCaseSense {    public static void main(String[] args) {       String stringSearch = "HI we are at java class.";       // this won't work because the pattern is in upper-case       System.out.println("Try this 1: " + stringSearch.matches(".*CLASS.*"));         // the magic (?i:X) syntax makes this search case-insensitive, so it returns true       System.out.println("Try this 2: " + stringSearch.matches("(?i:.*CLASS.*)"));    } }