Java Regex Patterns
Below are some common java regex patterns and their outputs.These java regex patterns are designed to test your understanding of regular expressions concept. Preparing for these java regex patterns will help you stand out and showcase your skill during technical interviews.
1.Pattern Matching with Regex
import java.util.regex.*;
public class RegexExample {
public static void main(String[] args) {
String text = “There are 123 numbers here”;
// Regular expression to match digits
String regex = “\\d+”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(text);
if (matcher.find()) {
System.out.println(“Found digits: ” + matcher.group());
} else {
System.out.println(“No digits found”);
}
}
}
Output:
Found digits: 123
2.Validating Email Address
import java.util.regex.*;
public class EmailValidator {
public static void main(String[] args) {
String email = “user@example.com”;
// Regular expression for validating email
String regex = “^[a-zA-Z0-9_+&*-]+(?:\\.[a-zA-Z0-9_+&*-]+)*@(?:[a-zA-Z0-9-]+\\.)+[a-zA-Z]{2,7}$”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(email);
if (matcher.matches()) {
System.out.println(“Valid email address”);
} else {
System.out.println(“Invalid email address”);
}
}
}
Output:
Valid email address
3.Splitting a String Based on a Pattern
import java.util.regex.*;
public class SplitStringExample {
public static void main(String[] args) {
String text = “This is an example, of string splitting. Let’s split!”;
// Regular expression to split by spaces, commas, or periods
String regex = “[ ,.]”;
String[] words = text.split(regex);
System.out.println(“Words after split:”);
for (String word : words) {
System.out.println(word);
}
}
}
Output:
Words after split:
This
is
an
example
of
string
splitting
Let's
Split
4.Replacing Text using Regex
import java.util.regex.*;
public class ReplaceDigitsExample {
public static void main(String[] args) {
String text = “My phone number is 123-456-7890”;
// Regular expression to match digits
String regex = “\\d”;
// Replace all digits with ‘#’
String replaced = text.replaceAll(regex, “#”);
System.out.println(“Replaced String: ” + replaced);
}
}
Output:
Replaced String: My phone number is ###-###-####
5.Extracting a Specific Part of a String
import java.util.regex.*;
public class ExtractDomain {
public static void main(String[] args) {
String url = “https://www.example.com/page”;
// Regular expression to match the domain
String regex = “https?://(www\\.)?([a-zA-Z0-9-]+)\\.”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(url);
if (matcher.find()) {
System.out.println(“Domain: ” + matcher.group(2)); // group(2) is the domain
} else {
System.out.println(“No domain found”);
}
}
}
Output:
Domain: example
6.Check if a String Contains a Pattern
import java.util.regex.*;
public class AlphanumericCheck {
public static void main(String[] args) {
String input = “Hello123”;
// Regular expression to match alphanumeric strings
String regex = “^[a-zA-Z0-9]+$”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(input);
if (matcher.matches()) {
System.out.println(“Valid alphanumeric string”);
} else {
System.out.println(“Invalid string”);
}
}
}
Output:
Valid alphanumeric string
7.Extract Phone Numbers from a Text
import java.util.regex.*;
public class ExtractPhoneNumber {
public static void main(String[] args) {
String text = “You can reach me at (123) 456-7890 or at (987) 654-3210.”;
// Regular expression to match phone numbers in (XXX) XXX-XXXX format
String regex = “\\(\\d{3}\\) \\d{3}-\\d{4}”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(text);
while (matcher.find()) {
System.out.println(“Found phone number: ” + matcher.group());
}
}
}
Output:
Found phone number: (123) 456-7890
Found phone number: (987) 654-3210
8.Validate a Strong Password
import java.util.regex.*;
public class PasswordValidator {
public static void main(String[] args) {
String password = “StrongP@ssw0rd”;
// Regular expression for a strong password
String regex = “^(?=.*[a-z])(?=.*[A-Z])(?=.*\\d)(?=.*[@$!%*?&])[A-Za-z\\d@$!%*?&]{8,}$”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(password);
if (matcher.matches()) {
System.out.println(“Valid strong password.”);
} else {
System.out.println(“Invalid password.”);
}
}
}
Output:
Valid strong password.
9.Replace Multiple Spaces with a Single Space
import java.util.regex.*;
public class ReplaceMultipleSpaces {
public static void main(String[] args) {
String text = “This is a string with multiple spaces.”;
// Regular expression to match multiple spaces
String regex = “\\s+”;
// Replace multiple spaces with a single space
String result = text.replaceAll(regex, ” “);
System.out.println(“Result: ” + result);
}
}
Output:
Result: This is a string with multiple spaces.
10.Extract Date from a String
import java.util.regex.*;
public class ExtractDate {
public static void main(String[] args) {
String text = “The meeting is scheduled for 05/12/2024 at 10 AM.”;
// Regular expression to match dates in MM/DD/YYYY format
String regex = “(\\d{2}/\\d{2}/\\d{4})”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(text);
if (matcher.find()) {
System.out.println(“Found date: ” + matcher.group());
} else {
System.out.println(“No date found.”);
}
}
}
Output:
Found date: 05/12/2024
11.Validate a Date in YYYY-MM-DD Format
import java.util.regex.*;
public class DateValidator {
public static void main(String[] args) {
String date = “2023-02-28”; // Test with different date inputs
// Regular expression to match a date in YYYY-MM-DD format
String regex = “^(?:19|20)\\d\\d-(0[1-9]|1[0-2])-(0[1-9]|[12][0-9]|3[01])$”;
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(date);
if (matcher.matches()) {
System.out.println(“Valid Date”);
} else {
System.out.println(“Invalid Date”);
}
}
}
Output:
Valid Date