The character classes in Java regular expression is defined using the square brackets "[ ]", this subexpression matches a single character from the specified or, set of possible characters.For example the regular expression [abc] matches a single character a or, b or, c. Similarly, "[a-z]" matches a single character from a to z.Similarly, the negation variant of the character class is defined as "[^ ]" (with ^ within the square braces), it matches a single character which is not in the specified or set of possible characters.For example the regular expression [^abc] matches a single character except a or, b ... Read More

To match/search a input data with multiple lines −Get the input string.Split it into an array of tokens by passing "\r?" as parameter to the split method.Compile the required regular expression using the compile() method of the pattern class.Retrieve the matcher object using the matcher() method.In the for loop find matches in the each element (new line) of the array using the find() method.Reset the input of the matcher to the next element of the array using the reset() method.Example Live Demoimport java.util.regex.Matcher; import java.util.regex.Pattern; public class MatchingText{    public static void main(String[] args) {       String input = ... Read More

The split() method of the String class accepts a regular expression, splits the current input text into tokens and returns them as a string array.Example Live Demoimport java.util.Scanner; public class Example{    public static void main(String[] args) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");       String input = sc.nextLine();       String[] strArray = input.split("\d");       for (int i=0; i

Named capturing groups allows you to reference the groups by names. Java started supporting captured groups since SE7.Example Live Demoimport java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class ReplaceAll{    public static void main(String[] args) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");       String input = sc.nextLine();       String regex = "(?[\d]{2})-(?[\d]{5})-(?[\d]{6})";       //Creating a pattern object       Pattern pattern = Pattern.compile(regex);       //Matching the compiled pattern in the String       Matcher matcher = pattern.matcher(input);       while (matcher.find()) { ... Read More

Once you compile the required regular expression and retrieved the matcher object by passing the input string as a parameter to the matcher() method.You can replace all the matched parts of the input string with another str4ing using the replaceAll() method of the Matcher class.This method accepts a string (replacement string) and replaces all the matches in the input string with it and returns the result.Example 1 Live Demoimport java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class ReplaceAll{    public static void main(String[] args) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");     ... Read More

To match a pattern within another match you need to compile the regular expression to match the outer pattern find the match retrieve the results and pass the results as input to the inner Matcher object.Example Live Demoimport java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class MatcherExample {    public static void main(String[] args) {       int start = 0, len = -1;       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");       String input = sc.nextLine();       String regexOuter = "(.*?)";       String regexInner = "\d+";   ... Read More

Java does not provide any method to retrieve the list of all matches we need to use Lists and add the results to it in the while loop.Example Live Demoimport java.util.ArrayList; import java.util.Iterator; import java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class ListOfMatches{    public static void main(String[] args) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");       String input = sc.nextLine();       String regex = "\d+";       //Creating a pattern object       Pattern pattern = Pattern.compile(regex);       ArrayList list = new ArrayList();   ... Read More

The start() method of the java.util.regex.Matcher class returns the starting position of the match (if a match occurred).Similarly, the end() method of the Matcher class returns the ending position of the match.Therefore, return value of the start() method will be the starting position of the match and the difference between the return values of the end() and start() methods will be the length of the match.Example Live Demoimport java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class MatcherExample {    public static void main(String[] args) {       int start = 0, len = -1;       Scanner sc = new ... Read More

Using capturing groups you can treat multiple characters as a single unit. You just need to place the characters to be grouped inside a set of parentheses. For example −(.*)(\d+)(.*)If you are trying to match multiple groups the match results of each group is captured. You can get the results a group by passing its respective group number to the group() method. 1, 2, 3 etc.. (from right to left) group 0 indicates the whole match.Example Live Demoimport java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class CapturingGroups {    public static void main( String args[] ) {       System.out.println("Enter input ... Read More

The meta character "\b" matches word boundaries. i.e. it matches before the first and after the last word characters and between word and non-word characters.Therefore to match a whole word you need to surround it between the word boundary meta characters as −\btest\bExample Live DemoFollowing Java example counts and prints the number of occurrences of the word test in the given input string.import java.util.Scanner; import java.util.regex.Matcher; import java.util.regex.Pattern; public class RegexExample1 {    public static void main(String[] args) {       Scanner sc = new Scanner(System.in);       System.out.println("Enter input text: ");       String input = sc.nextLine(); ... Read More