Regular Expression Patterns

// Email validation patterns

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Email {

    public static void main(String[] args) {
        // Basic email pattern
        String basicEmail = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$";

        String[] emails = {
            "user@example.com",
            "first.last@domain.co.uk",
            "user+tag@example.org",
            "invalid@",
            "@invalid.com",
            "no-at-sign.com",
            "user@domain",
            "user@domain.c"
        };

        System.out.println("Basic email validation:");
        Pattern pattern = Pattern.compile(basicEmail);
        for (String email : emails) {
            boolean valid = pattern.matcher(email).matches();
            System.out.println("  " + email + ": " + valid);
        }

        // Extract email parts
        String emailPattern = "^([a-zA-Z0-9._%+-]+)@([a-zA-Z0-9.-]+)\\.([a-zA-Z]{2,})$";
        Pattern extractPattern = Pattern.compile(emailPattern);

        System.out.println("\nExtract email parts:");
        String testEmail = "john.doe@example.com";
        Matcher matcher = extractPattern.matcher(testEmail);

        if (matcher.matches()) {
            System.out.println("  Email: " + testEmail);
            System.out.println("  Username: " + matcher.group(1));
            System.out.println("  Domain: " + matcher.group(2));
            System.out.println("  TLD: " + matcher.group(3));
        }

        // Find all emails in text
        String text = """
            Contact us at support@example.com or sales@company.org.
            For urgent matters, email admin@service.net immediately.
            """;

        Pattern findPattern = Pattern.compile("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}");
        Matcher findMatcher = findPattern.matcher(text);

        System.out.println("\nEmails found in text:");
        while (findMatcher.find()) {
            System.out.println("  " + findMatcher.group());
        }

        // More strict pattern (requires valid TLD length)
        String strictEmail = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,6}$";
        Pattern strictPattern = Pattern.compile(strictEmail);

        System.out.println("\nStrict validation:");
        String[] testEmails = {
            "user@domain.com",
            "user@domain.co",
            "user@domain.technology"  // 10 chars TLD
        };

        for (String email : testEmails) {
            boolean valid = strictPattern.matcher(email).matches();
            System.out.println("  " + email + ": " + valid);
        }
    }

}

// Email validation patterns

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Email {

    public static void main(String[] args) {
        // Basic email pattern
        String basicEmail = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}$";

        String[] emails = {
            "user@example.com",
            "first.last@domain.co.uk",
            "user+tag@example.org",
            "invalid@",
            "@invalid.com",
            "no-at-sign.com",
            "user@domain",
            "user@domain.c"
        };

        System.out.println("Basic email validation:");
        Pattern pattern = Pattern.compile(basicEmail);
        for (String email : emails) {
            boolean valid = pattern.matcher(email).matches();
            System.out.println("  " + email + ": " + valid);
        }

        // Extract email parts
        String emailPattern = "^([a-zA-Z0-9._%+-]+)@([a-zA-Z0-9.-]+)\\.([a-zA-Z]{2,})$";
        Pattern extractPattern = Pattern.compile(emailPattern);

        System.out.println("\nExtract email parts:");
        String testEmail = "bad-address";
        Matcher matcher = extractPattern.matcher(testEmail);

        if (matcher.matches()) {
            System.out.println("  Email: " + testEmail);
            System.out.println("  Username: " + matcher.group(1));
            System.out.println("  Domain: " + matcher.group(2));
            System.out.println("  TLD: " + matcher.group(3));
        }

        // Find all emails in text
        String text = """
            Contact us at support@example.com or sales@company.org.
            For urgent matters, email admin@service.net immediately.
            """;

        Pattern findPattern = Pattern.compile("[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}");
        Matcher findMatcher = findPattern.matcher(text);

        System.out.println("\nEmails found in text:");
        while (findMatcher.find()) {
            System.out.println("  " + findMatcher.group());
        }

        // More strict pattern (requires valid TLD length)
        String strictEmail = "^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,6}$";
        Pattern strictPattern = Pattern.compile(strictEmail);

        System.out.println("\nStrict validation:");
        String[] testEmails = {
            "user@domain.com",
            "user@domain.co",
            "user@domain.technology"  // 10 chars TLD
        };

        for (String email : testEmails) {
            boolean valid = strictPattern.matcher(email).matches();
            System.out.println("  " + email + ": " + valid);
        }
    }

}

// Phone number patterns

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Phone {

    public static void main(String[] args) {
        // US phone formats
        String[] patterns = {
            "\\(\\d{3}\\)\\s\\d{3}-\\d{4}",  // (123) 456-7890
            "\\d{3}-\\d{3}-\\d{4}",           // 123-456-7890
            "\\d{10}"                         // 1234567890
        };

        String[] phones = {
            "(555) 123-4567",
            "555-123-4567",
            "5551234567",
            "(555)123-4567",  // no space
            "555.123.4567",
            "invalid"
        };

        System.out.println("Phone validation:");
        for (int i = 0; i < patterns.length; i++) {
            System.out.println("\nPattern " + (i+1) + ":");
            Pattern p = Pattern.compile(patterns[i]);
            for (String phone : phones) {
                boolean valid = p.matcher(phone).matches();
                System.out.println("  " + phone + ": " + valid);
            }
        }

        // Combined pattern (any format)
        String anyFormat = "^(\\(\\d{3}\\)\\s?|\\d{3}-)?\\d{3}-?\\d{4}$";
        Pattern anyPattern = Pattern.compile(anyFormat);

        System.out.println("\nCombined pattern:");
        for (String phone : phones) {
            boolean valid = anyPattern.matcher(phone).matches();
            System.out.println("  " + phone + ": " + valid);
        }

        // Extract phone parts
        String extractPattern = "\\((\\d{3})\\)\\s(\\d{3})-(\\d{4})";
        Pattern extract = Pattern.compile(extractPattern);

        String testPhone = "(555) 123-4567";
        Matcher matcher = extract.matcher(testPhone);

        if (matcher.matches()) {
            System.out.println("\nExtracted parts from " + testPhone + ":");
            System.out.println("  Area code: " + matcher.group(1));
            System.out.println("  Exchange: " + matcher.group(2));
            System.out.println("  Number: " + matcher.group(3));
        }

        // Find all phones in text
        String text = """
            Call us at (555) 123-4567 or 555-987-6543.
            Emergency: (999) 911-0000
            """;

        Pattern findPattern = Pattern.compile("\\(?\\d{3}\\)?[-\\s]?\\d{3}-\\d{4}");
        Matcher findMatcher = findPattern.matcher(text);

        System.out.println("\nPhones found in text:");
        while (findMatcher.find()) {
            System.out.println("  " + findMatcher.group());
        }

        // International format (basic)
        String intlPattern = "^\\+?\\d{1,3}[-\\s]?\\(?\\d{1,4}\\)?[-\\s]?\\d{1,4}[-\\s]?\\d{1,9}$";
        Pattern intlP = Pattern.compile(intlPattern);

        String[] intlPhones = {
            "+1 (555) 123-4567",
            "+44 20 7123 4567",
            "+81 3-1234-5678"
        };

        System.out.println("\nInternational phones:");
        for (String phone : intlPhones) {
            boolean valid = intlP.matcher(phone).matches();
            System.out.println("  " + phone + ": " + valid);
        }
    }

}

// Phone number patterns

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Phone {

    public static void main(String[] args) {
        // US phone formats
        String[] patterns = {
            "\\(\\d{3}\\)\\s\\d{3}-\\d{4}",  // (123) 456-7890
            "\\d{3}-\\d{3}-\\d{4}",           // 123-456-7890
            "\\d{10}"                         // 1234567890
        };

        String[] phones = {
            "(555) 123-4567",
            "555-123-4567",
            "5551234567",
            "(555)123-4567",  // no space
            "555.123.4567",
            "invalid"
        };

        System.out.println("Phone validation:");
        for (int i = 0; i < patterns.length; i++) {
            System.out.println("\nPattern " + (i+1) + ":");
            Pattern p = Pattern.compile(patterns[i]);
            for (String phone : phones) {
                boolean valid = p.matcher(phone).matches();
                System.out.println("  " + phone + ": " + valid);
            }
        }

        // Combined pattern (any format)
        String anyFormat = "^(\\(\\d{3}\\)\\s?|\\d{3}-)?\\d{3}-?\\d{4}$";
        Pattern anyPattern = Pattern.compile(anyFormat);

        System.out.println("\nCombined pattern:");
        for (String phone : phones) {
            boolean valid = anyPattern.matcher(phone).matches();
            System.out.println("  " + phone + ": " + valid);
        }

        // Extract phone parts
        String extractPattern = "\\((\\d{3})\\)\\s(\\d{3})-(\\d{4})";
        Pattern extract = Pattern.compile(extractPattern);

        String testPhone = "555-123-4567";
        Matcher matcher = extract.matcher(testPhone);

        if (matcher.matches()) {
            System.out.println("\nExtracted parts from " + testPhone + ":");
            System.out.println("  Area code: " + matcher.group(1));
            System.out.println("  Exchange: " + matcher.group(2));
            System.out.println("  Number: " + matcher.group(3));
        }

        // Find all phones in text
        String text = """
            Call us at (555) 123-4567 or 555-987-6543.
            Emergency: (999) 911-0000
            """;

        Pattern findPattern = Pattern.compile("\\(?\\d{3}\\)?[-\\s]?\\d{3}-\\d{4}");
        Matcher findMatcher = findPattern.matcher(text);

        System.out.println("\nPhones found in text:");
        while (findMatcher.find()) {
            System.out.println("  " + findMatcher.group());
        }

        // International format (basic)
        String intlPattern = "^\\+?\\d{1,3}[-\\s]?\\(?\\d{1,4}\\)?[-\\s]?\\d{1,4}[-\\s]?\\d{1,9}$";
        Pattern intlP = Pattern.compile(intlPattern);

        String[] intlPhones = {
            "+1 (555) 123-4567",
            "+44 20 7123 4567",
            "+81 3-1234-5678"
        };

        System.out.println("\nInternational phones:");
        for (String phone : intlPhones) {
            boolean valid = intlP.matcher(phone).matches();
            System.out.println("  " + phone + ": " + valid);
        }
    }

}

// URL patterns

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Url {

    public static void main(String[] args) {
        // Basic URL pattern
        String urlPattern = "^https?://[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}.*$";

        String[] urls = {
            "https://example.com",
            "http://www.example.com",
            "https://sub.example.co.uk",
            "https://example.com/path",
            "https://example.com/path?key=value",
            "ftp://example.com",  // wrong protocol
            "example.com",        // missing protocol
            "https://localhost"   // no TLD
        };

        System.out.println("URL validation:");
        Pattern pattern = Pattern.compile(urlPattern);
        for (String url : urls) {
            boolean valid = pattern.matcher(url).matches();
            System.out.println("  " + url + ": " + valid);
        }

        // Extract URL parts
        String extractPattern = "^(https?)://([a-zA-Z0-9.-]+)(/.*)?$";
        Pattern extractP = Pattern.compile(extractPattern);

        String testUrl = "https://www.example.com/path/to/page";
        Matcher matcher = extractP.matcher(testUrl);

        if (matcher.matches()) {
            System.out.println("\nExtracted parts from " + testUrl + ":");
            System.out.println("  Protocol: " + matcher.group(1));
            System.out.println("  Domain: " + matcher.group(2));
            System.out.println("  Path: " + (matcher.group(3) != null ? matcher.group(3) : "/"));
        }

        // More detailed extraction
        String detailPattern = "^(https?)://([^:/]+)(:(\\d+))?(/.*)?$";
        Pattern detailP = Pattern.compile(detailPattern);

        String[] testUrls = {
            "https://example.com:8080/path",
            "http://localhost:3000/api",
            "https://example.com/page"
        };

        System.out.println("\nDetailed URL parsing:");
        for (String url : testUrls) {
            Matcher m = detailP.matcher(url);
            if (m.matches()) {
                System.out.println("  " + url);
                System.out.println("    Protocol: " + m.group(1));
                System.out.println("    Host: " + m.group(2));
                System.out.println("    Port: " + (m.group(4) != null ? m.group(4) : "default"));
                System.out.println("    Path: " + (m.group(5) != null ? m.group(5) : "/"));
            }
        }

        // Find all URLs in text
        String text = """
            Visit https://example.com for more info.
            Check out http://test.org/page and https://another.site/path?q=search
            """;

        Pattern findPattern = Pattern.compile("https?://[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}[^\\s]*");
        Matcher findMatcher = findPattern.matcher(text);

        System.out.println("\nURLs found in text:");
        while (findMatcher.find()) {
            System.out.println("  " + findMatcher.group());
        }

        // Query parameters
        String queryPattern = "[?&]([^=]+)=([^&]+)";
        String urlWithQuery = "https://example.com/search?q=regex&lang=java&page=1";

        Pattern queryP = Pattern.compile(queryPattern);
        Matcher queryM = queryP.matcher(urlWithQuery);

        System.out.println("\nQuery parameters from: " + urlWithQuery);
        while (queryM.find()) {
            System.out.println("  " + queryM.group(1) + " = " + queryM.group(2));
        }
    }

}

// URL patterns

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Url {

    public static void main(String[] args) {
        // Basic URL pattern
        String urlPattern = "^https?://[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}.*$";

        String[] urls = {
            "https://example.com",
            "http://www.example.com",
            "https://sub.example.co.uk",
            "https://example.com/path",
            "https://example.com/path?key=value",
            "ftp://example.com",  // wrong protocol
            "example.com",        // missing protocol
            "https://localhost"   // no TLD
        };

        System.out.println("URL validation:");
        Pattern pattern = Pattern.compile(urlPattern);
        for (String url : urls) {
            boolean valid = pattern.matcher(url).matches();
            System.out.println("  " + url + ": " + valid);
        }

        // Extract URL parts
        String extractPattern = "^(https?)://([a-zA-Z0-9.-]+)(/.*)?$";
        Pattern extractP = Pattern.compile(extractPattern);

        String testUrl = "http://example.org";
        Matcher matcher = extractP.matcher(testUrl);

        if (matcher.matches()) {
            System.out.println("\nExtracted parts from " + testUrl + ":");
            System.out.println("  Protocol: " + matcher.group(1));
            System.out.println("  Domain: " + matcher.group(2));
            System.out.println("  Path: " + (matcher.group(3) != null ? matcher.group(3) : "/"));
        }

        // More detailed extraction
        String detailPattern = "^(https?)://([^:/]+)(:(\\d+))?(/.*)?$";
        Pattern detailP = Pattern.compile(detailPattern);

        String[] testUrls = {
            "https://example.com:8080/path",
            "http://localhost:3000/api",
            "https://example.com/page"
        };

        System.out.println("\nDetailed URL parsing:");
        for (String url : testUrls) {
            Matcher m = detailP.matcher(url);
            if (m.matches()) {
                System.out.println("  " + url);
                System.out.println("    Protocol: " + m.group(1));
                System.out.println("    Host: " + m.group(2));
                System.out.println("    Port: " + (m.group(4) != null ? m.group(4) : "default"));
                System.out.println("    Path: " + (m.group(5) != null ? m.group(5) : "/"));
            }
        }

        // Find all URLs in text
        String text = """
            Visit https://example.com for more info.
            Check out http://test.org/page and https://another.site/path?q=search
            """;

        Pattern findPattern = Pattern.compile("https?://[a-zA-Z0-9.-]+\\.[a-zA-Z]{2,}[^\\s]*");
        Matcher findMatcher = findPattern.matcher(text);

        System.out.println("\nURLs found in text:");
        while (findMatcher.find()) {
            System.out.println("  " + findMatcher.group());
        }

        // Query parameters
        String queryPattern = "[?&]([^=]+)=([^&]+)";
        String urlWithQuery = "https://example.com/search?q=regex&lang=java&page=1";

        Pattern queryP = Pattern.compile(queryPattern);
        Matcher queryM = queryP.matcher(urlWithQuery);

        System.out.println("\nQuery parameters from: " + urlWithQuery);
        while (queryM.find()) {
            System.out.println("  " + queryM.group(1) + " = " + queryM.group(2));
        }
    }

}

// Text extraction with regex

import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.util.ArrayList;
import java.util.List;

public class Extraction {

    public static List<String> extractHashtags(String text) {
        List<String> hashtags = new ArrayList<>();
        Pattern pattern = Pattern.compile("#\\w+");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            hashtags.add(matcher.group());
        }
        return hashtags;
    }

    public static List<String> extractMentions(String text) {
        List<String> mentions = new ArrayList<>();
        Pattern pattern = Pattern.compile("@\\w+");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            mentions.add(matcher.group());
        }
        return mentions;
    }

    public static List<Double> extractNumbers(String text) {
        List<Double> numbers = new ArrayList<>();
        Pattern pattern = Pattern.compile("-?\\d+\\.?\\d*");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            numbers.add(Double.parseDouble(matcher.group()));
        }
        return numbers;
    }

    public static List<String> extractDates(String text) {
        List<String> dates = new ArrayList<>();
        // YYYY-MM-DD format
        Pattern pattern = Pattern.compile("\\d{4}-\\d{2}-\\d{2}");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            dates.add(matcher.group());
        }
        return dates;
    }

    public static void main(String[] args) {
        // Social media text
        String tweet = """
            Loving #java and #regex! Thanks @copilot for the help.
            Check out #programming tips at https://example.com
            Mentions: @user1 @user2 #coding
            """;

        System.out.println("Social media extraction:");
        System.out.println("Hashtags: " + extractHashtags(tweet));
        System.out.println("Mentions: " + extractMentions(tweet));

        // Numbers
        String dataText = "Prices: $19.99, $5.50, and $100. Temperature: -5.5°C";
        System.out.println("\nNumbers extraction:");
        System.out.println("Numbers: " + extractNumbers(dataText));

        // Dates
        String logText = """
            2025-01-29: Error occurred
            2025-01-30: Fixed bug
            2025-02-01: Deployed
            """;
        System.out.println("\nDates extraction:");
        System.out.println("Dates: " + extractDates(logText));

        // IP addresses
        String serverLog = "Requests from 192.168.1.1, 10.0.0.5, and 172.16.0.10";
        Pattern ipPattern = Pattern.compile("\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}");
        Matcher ipMatcher = ipPattern.matcher(serverLog);

        System.out.println("\nIP addresses:");
        while (ipMatcher.find()) {
            System.out.println("  " + ipMatcher.group());
        }

        // Extract quoted strings
        String quoteText = "He said \"Hello\" and she replied \"Hi there!\"";
        Pattern quotePattern = Pattern.compile("\"([^\"]+)\"");
        Matcher quoteMatcher = quotePattern.matcher(quoteText);

        System.out.println("\nQuoted strings:");
        while (quoteMatcher.find()) {
            System.out.println("  " + quoteMatcher.group(1));
        }

        // Key-value pairs
        String config = "name=John age=30 city=NYC email=john@example.com";
        Pattern kvPattern = Pattern.compile("(\\w+)=(\\S+)");
        Matcher kvMatcher = kvPattern.matcher(config);

        System.out.println("\nKey-value pairs:");
        while (kvMatcher.find()) {
            System.out.println("  " + kvMatcher.group(1) + " = " + kvMatcher.group(2));
        }

        // HTML tags (simple)
        String html = "<div>Content</div><span>Text</span>";
        Pattern tagPattern = Pattern.compile("<(\\w+)>([^<]+)</\\1>");
        Matcher tagMatcher = tagPattern.matcher(html);

        System.out.println("\nHTML content:");
        while (tagMatcher.find()) {
            System.out.println("  <" + tagMatcher.group(1) + ">: " + tagMatcher.group(2));
        }
    }

}

// Text extraction with regex

import java.util.regex.Pattern;
import java.util.regex.Matcher;
import java.util.ArrayList;
import java.util.List;

public class Extraction {

    public static List<String> extractHashtags(String text) {
        List<String> hashtags = new ArrayList<>();
        Pattern pattern = Pattern.compile("#\\w+");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            hashtags.add(matcher.group());
        }
        return hashtags;
    }

    public static List<String> extractMentions(String text) {
        List<String> mentions = new ArrayList<>();
        Pattern pattern = Pattern.compile("@\\w+");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            mentions.add(matcher.group());
        }
        return mentions;
    }

    public static List<Double> extractNumbers(String text) {
        List<Double> numbers = new ArrayList<>();
        Pattern pattern = Pattern.compile("-?\\d+\\.?\\d*");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            numbers.add(Double.parseDouble(matcher.group()));
        }
        return numbers;
    }

    public static List<String> extractDates(String text) {
        List<String> dates = new ArrayList<>();
        // YYYY-MM-DD format
        Pattern pattern = Pattern.compile("\\d{4}-\\d{2}-\\d{2}");
        Matcher matcher = pattern.matcher(text);

        while (matcher.find()) {
            dates.add(matcher.group());
        }
        return dates;
    }

    public static void main(String[] args) {
        // Social media text
        String tweet = """
            Loving #java and #regex! Thanks @copilot for the help.
            Check out #programming tips at https://example.com
            Mentions: @user1 @user2 #coding
            """;

        System.out.println("Social media extraction:");
        System.out.println("Hashtags: " + extractHashtags(tweet));
        System.out.println("Mentions: " + extractMentions(tweet));

        // Numbers
        String dataText = "Prices: $19.99, $5.50, and $100. Temperature: -5.5°C";
        System.out.println("\nNumbers extraction:");
        System.out.println("Numbers: " + extractNumbers(dataText));

        // Dates
        String logText = """
            2025-01-29: Error occurred
            2025-01-30: Fixed bug
            2025-02-01: Deployed
            """;
        System.out.println("\nDates extraction:");
        System.out.println("Dates: " + extractDates(logText));

        // IP addresses
        String serverLog = "Requests from 192.168.1.1, 10.0.0.5, and 172.16.0.10";
        Pattern ipPattern = Pattern.compile("\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}\\.\\d{1,3}");
        Matcher ipMatcher = ipPattern.matcher(serverLog);

        System.out.println("\nIP addresses:");
        while (ipMatcher.find()) {
            System.out.println("  " + ipMatcher.group());
        }

        // Extract quoted strings
        String quoteText = "He said \"Hello\" and she replied \"Hi there!\"";
        Pattern quotePattern = Pattern.compile("\"([^\"]+)\"");
        Matcher quoteMatcher = quotePattern.matcher(quoteText);

        System.out.println("\nQuoted strings:");
        while (quoteMatcher.find()) {
            System.out.println("  " + quoteMatcher.group(1));
        }

        // Key-value pairs
        String config = "name=Ada role=admin city=London";
        Pattern kvPattern = Pattern.compile("(\\w+)=(\\S+)");
        Matcher kvMatcher = kvPattern.matcher(config);

        System.out.println("\nKey-value pairs:");
        while (kvMatcher.find()) {
            System.out.println("  " + kvMatcher.group(1) + " = " + kvMatcher.group(2));
        }

        // HTML tags (simple)
        String html = "<div>Content</div><span>Text</span>";
        Pattern tagPattern = Pattern.compile("<(\\w+)>([^<]+)</\\1>");
        Matcher tagMatcher = tagPattern.matcher(html);

        System.out.println("\nHTML content:");
        while (tagMatcher.find()) {
            System.out.println("  <" + tagMatcher.group(1) + ">: " + tagMatcher.group(2));
        }
    }

}

// String splitting with regex

import java.util.Arrays;
import java.util.regex.Pattern;

public class Splitting {

    public static void main(String[] args) {
        // Split by comma
        String csv1 = "apple,banana,cherry";
        String[] parts1 = csv1.split(",");
        System.out.println("Split by comma:");
        System.out.println("  " + Arrays.toString(parts1));

        // Split by whitespace
        String text1 = "one two  three   four";
        String[] parts2 = text1.split("\\s+");
        System.out.println("\nSplit by whitespace:");
        System.out.println("  " + Arrays.toString(parts2));

        // Split by multiple delimiters
        String text2 = "apple;banana,cherry:orange";
        String[] parts3 = text2.split("[;,:]+");
        System.out.println("\nSplit by multiple delimiters:");
        System.out.println("  " + Arrays.toString(parts3));

        // Split with limit
        String text3 = "one,two,three,four,five";
        String[] parts4 = text3.split(",", 3);
        System.out.println("\nSplit with limit (3):");
        System.out.println("  " + Arrays.toString(parts4));

        // Split preserving delimiters (lookahead)
        String text4 = "one,two,three";
        String[] parts5 = text4.split("(?=,)");
        System.out.println("\nSplit preserving delimiters:");
        System.out.println("  " + Arrays.toString(parts5));

        // Split by word boundaries
        String text5 = "hello-world_test";
        String[] parts6 = text5.split("[-_]");
        System.out.println("\nSplit by hyphens and underscores:");
        System.out.println("  " + Arrays.toString(parts6));

        // Split sentences
        String paragraph = "First sentence. Second sentence! Third question?";
        String[] sentences = paragraph.split("[.!?]\\s*");
        System.out.println("\nSplit sentences:");
        for (int i = 0; i < sentences.length; i++) {
            System.out.println("  " + (i+1) + ": " + sentences[i]);
        }

        // Split keeping empty strings
        String text6 = "a,,b,,,c";
        String[] parts7 = text6.split(",");
        String[] parts8 = text6.split(",", -1);
        System.out.println("\nDefault (discard trailing empty):");
        System.out.println("  " + Arrays.toString(parts7));
        System.out.println("Keep empty strings (limit = -1):");
        System.out.println("  " + Arrays.toString(parts8));

        // Split path
        String path = "C:\\Users\\John\\Documents\\file.txt";
        String[] pathParts = path.split("\\\\");
        System.out.println("\nSplit Windows path:");
        System.out.println("  " + Arrays.toString(pathParts));

        // Split by digits
        String text7 = "abc123def456ghi";
        String[] parts9 = text7.split("\\d+");
        System.out.println("\nSplit by digits:");
        System.out.println("  " + Arrays.toString(parts9));

        // Compiled pattern for reuse
        Pattern pattern = Pattern.compile("\\s*,\\s*");  // comma with optional spaces
        String text8 = "a, b,c ,d , e";
        String[] parts10 = pattern.split(text8);
        System.out.println("\nSplit CSV with spaces:");
        System.out.println("  " + Arrays.toString(parts10));

        // Split complex: key=value pairs
        String config = "name=John;age=30;city=NYC";
        String[] pairs = config.split(";");
        System.out.println("\nParse config:");
        for (String pair : pairs) {
            String[] kv = pair.split("=");
            System.out.println("  " + kv[0] + " -> " + kv[1]);
        }
    }

}

// String splitting with regex

import java.util.Arrays;
import java.util.regex.Pattern;

public class Splitting {

    public static void main(String[] args) {
        // Split by comma
        String csv1 = "red,green,blue";
        String[] parts1 = csv1.split(",");
        System.out.println("Split by comma:");
        System.out.println("  " + Arrays.toString(parts1));

        // Split by whitespace
        String text1 = "one two  three   four";
        String[] parts2 = text1.split("\\s+");
        System.out.println("\nSplit by whitespace:");
        System.out.println("  " + Arrays.toString(parts2));

        // Split by multiple delimiters
        String text2 = "apple;banana,cherry:orange";
        String[] parts3 = text2.split("[;,:]+");
        System.out.println("\nSplit by multiple delimiters:");
        System.out.println("  " + Arrays.toString(parts3));

        // Split with limit
        String text3 = "one,two,three,four,five";
        String[] parts4 = text3.split(",", 3);
        System.out.println("\nSplit with limit (3):");
        System.out.println("  " + Arrays.toString(parts4));

        // Split preserving delimiters (lookahead)
        String text4 = "one,two,three";
        String[] parts5 = text4.split("(?=,)");
        System.out.println("\nSplit preserving delimiters:");
        System.out.println("  " + Arrays.toString(parts5));

        // Split by word boundaries
        String text5 = "hello-world_test";
        String[] parts6 = text5.split("[-_]");
        System.out.println("\nSplit by hyphens and underscores:");
        System.out.println("  " + Arrays.toString(parts6));

        // Split sentences
        String paragraph = "First sentence. Second sentence! Third question?";
        String[] sentences = paragraph.split("[.!?]\\s*");
        System.out.println("\nSplit sentences:");
        for (int i = 0; i < sentences.length; i++) {
            System.out.println("  " + (i+1) + ": " + sentences[i]);
        }

        // Split keeping empty strings
        String text6 = "a,,b,,,c";
        String[] parts7 = text6.split(",");
        String[] parts8 = text6.split(",", -1);
        System.out.println("\nDefault (discard trailing empty):");
        System.out.println("  " + Arrays.toString(parts7));
        System.out.println("Keep empty strings (limit = -1):");
        System.out.println("  " + Arrays.toString(parts8));

        // Split path
        String path = "C:\\Users\\John\\Documents\\file.txt";
        String[] pathParts = path.split("\\\\");
        System.out.println("\nSplit Windows path:");
        System.out.println("  " + Arrays.toString(pathParts));

        // Split by digits
        String text7 = "abc123def456ghi";
        String[] parts9 = text7.split("\\d+");
        System.out.println("\nSplit by digits:");
        System.out.println("  " + Arrays.toString(parts9));

        // Compiled pattern for reuse
        Pattern pattern = Pattern.compile("\\s*,\\s*");  // comma with optional spaces
        String text8 = "a, b,c ,d , e";
        String[] parts10 = pattern.split(text8);
        System.out.println("\nSplit CSV with spaces:");
        System.out.println("  " + Arrays.toString(parts10));

        // Split complex: key=value pairs
        String config = "name=John;age=30;city=NYC";
        String[] pairs = config.split(";");
        System.out.println("\nParse config:");
        for (String pair : pairs) {
            String[] kv = pair.split("=");
            System.out.println("  " + kv[0] + " -> " + kv[1]);
        }
    }

}

// String replacement with regex

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Replacement {

    public static void main(String[] args) {
        // Simple replaceAll
        String text1 = "Hello World, Hello Java";
        String result1 = text1.replaceAll("Hello", "Hi");
        System.out.println("Original: " + text1);
        System.out.println("Replaced: " + result1);

        // Replace with pattern
        String text2 = "Call 555-1234 or 555-5678";
        String result2 = text2.replaceAll("\\d{3}-\\d{4}", "XXX-XXXX");
        System.out.println("\nMask phone numbers:");
        System.out.println("Original: " + text2);
        System.out.println("Masked: " + result2);

        // Replace with groups
        String text3 = "2025-01-29";
        String result3 = text3.replaceAll("(\\d{4})-(\\d{2})-(\\d{2})", "$2/$3/$1");
        System.out.println("\nReformat date:");
        System.out.println("Original (YYYY-MM-DD): " + text3);
        System.out.println("Reformatted (MM/DD/YYYY): " + result3);

        // Remove extra whitespace
        String text4 = "Too    many     spaces";
        String result4 = text4.replaceAll("\\s+", " ");
        System.out.println("\nNormalize whitespace:");
        System.out.println("Original: '" + text4 + "'");
        System.out.println("Normalized: '" + result4 + "'");

        // Remove HTML tags
        String html = "<p>Hello <b>World</b></p>";
        String result5 = html.replaceAll("<[^>]+>", "");
        System.out.println("\nRemove HTML:");
        System.out.println("Original: " + html);
        System.out.println("Clean: " + result5);

        // Censor profanity (example)
        String text6 = "This is bad and terrible";
        String result6 = text6.replaceAll("\\b(bad|terrible)\\b", "***");
        System.out.println("\nCensor words:");
        System.out.println("Original: " + text6);
        System.out.println("Censored: " + result6);

        // Format currency
        String text7 = "Price: 1234.56";
        String result7 = text7.replaceAll("(\\d+)", "\\$$1");
        System.out.println("\nAdd currency:");
        System.out.println("Original: " + text7);
        System.out.println("Formatted: " + result7);

        // Matcher with appendReplacement (more control)
        String text8 = "one two three";
        Pattern pattern = Pattern.compile("(\\w+)");
        Matcher matcher = pattern.matcher(text8);
        StringBuffer result = new StringBuffer();

        while (matcher.find()) {
            String word = matcher.group(1);
            matcher.appendReplacement(result, word.toUpperCase());
        }
        matcher.appendTail(result);

        System.out.println("\nCustom replacement:");
        System.out.println("Original: " + text8);
        System.out.println("Uppercase: " + result);

        // Advanced: swap first and last name
        String names = "John Doe, Jane Smith, Bob Johnson";
        String result9 = names.replaceAll("(\\w+)\\s(\\w+)", "$2, $1");
        System.out.println("\nSwap names:");
        System.out.println("Original: " + names);
        System.out.println("Swapped: " + result9);
    }

}

// String replacement with regex

import java.util.regex.Pattern;
import java.util.regex.Matcher;

public class Replacement {

    public static void main(String[] args) {
        // Simple replaceAll
        String text1 = "Hello World, Hello Java";
        String result1 = text1.replaceAll("Hello", "Hi");
        System.out.println("Original: " + text1);
        System.out.println("Replaced: " + result1);

        // Replace with pattern
        String text2 = "Call 555-1234 or 555-5678";
        String result2 = text2.replaceAll("\\d{3}-\\d{4}", "XXX-XXXX");
        System.out.println("\nMask phone numbers:");
        System.out.println("Original: " + text2);
        System.out.println("Masked: " + result2);

        // Replace with groups
        String text3 = "2025-01-29";
        String result3 = text3.replaceAll("(\\d{4})-(\\d{2})-(\\d{2})", "$2/$3/$1");
        System.out.println("\nReformat date:");
        System.out.println("Original (YYYY-MM-DD): " + text3);
        System.out.println("Reformatted (MM/DD/YYYY): " + result3);

        // Remove extra whitespace
        String text4 = "Too    many     spaces";
        String result4 = text4.replaceAll("\\s+", " ");
        System.out.println("\nNormalize whitespace:");
        System.out.println("Original: '" + text4 + "'");
        System.out.println("Normalized: '" + result4 + "'");

        // Remove HTML tags
        String html = "<p>Hello <b>World</b></p>";
        String result5 = html.replaceAll("<[^>]+>", "");
        System.out.println("\nRemove HTML:");
        System.out.println("Original: " + html);
        System.out.println("Clean: " + result5);

        // Censor profanity (example)
        String text6 = "bad code can become better";
        String result6 = text6.replaceAll("\\b(bad|terrible)\\b", "***");
        System.out.println("\nCensor words:");
        System.out.println("Original: " + text6);
        System.out.println("Censored: " + result6);

        // Format currency
        String text7 = "Price: 1234.56";
        String result7 = text7.replaceAll("(\\d+)", "\\$$1");
        System.out.println("\nAdd currency:");
        System.out.println("Original: " + text7);
        System.out.println("Formatted: " + result7);

        // Matcher with appendReplacement (more control)
        String text8 = "one two three";
        Pattern pattern = Pattern.compile("(\\w+)");
        Matcher matcher = pattern.matcher(text8);
        StringBuffer result = new StringBuffer();

        while (matcher.find()) {
            String word = matcher.group(1);
            matcher.appendReplacement(result, word.toUpperCase());
        }
        matcher.appendTail(result);

        System.out.println("\nCustom replacement:");
        System.out.println("Original: " + text8);
        System.out.println("Uppercase: " + result);

        // Advanced: swap first and last name
        String names = "John Doe, Jane Smith, Bob Johnson";
        String result9 = names.replaceAll("(\\w+)\\s(\\w+)", "$2, $1");
        System.out.println("\nSwap names:");
        System.out.println("Original: " + names);
        System.out.println("Swapped: " + result9);
    }

}