Extract all integers from the given String in Java

// Java program to extract integers from a string 
// using regex

import java.util.regex.*;
import java.util.*;

public class Extract {
  
    public static void main(String[] args) {
      
        String i = "Java 123 is a Programming 456 Language.";

        // Compile the regex to match integers
        Pattern pattern = Pattern.compile("\\d+");
        Matcher matcher = pattern.matcher(i);

        // Extract integers
        List<Integer> n = new ArrayList<>();
        while (matcher.find()) {
            n.add(Integer.parseInt(matcher.group()));
        }

        System.out.println("" + n);
    }
}

// Java program to extract integers from a given string

public class Extract {

    public static void main(String[] args) {
      
        String s = "abc123def456ghi";
        StringBuilder r = new StringBuilder();

        boolean wasDigit = false; // Flag to track if the previous character was a digit

        // Iterate through each character in the string
        for (char c : s.toCharArray()) {

            if (Character.isDigit(c)) {
                r.append(c);  
                wasDigit = true; // Mark that we are in a digit sequence
            } else if (wasDigit) {
              
                // Append a space only after a sequence of digits ends
                r.append(" ");
                wasDigit = false; // Reset flag for non-digit characters
            }
        }

        // Convert StringBuilder to String and print
        String a = r.toString().trim();
        System.out.println(a.isEmpty() ? "-1" : a);
    }
}

// Java program to demonstrate extracting integers from a given string
public class GFG {

    // Function to return the modified string
    static String extractInt(String s) {
        
        // Replacing every non-digit character with a space (" ")
        s = s.replaceAll("[^\\d]", " ");

        // Remove extra spaces from the beginning and the end of the string
        s = s.trim();

        // Replace all consecutive white spaces with a single space
        s = s.replaceAll(" +", " ");

        // Return -1 if the string is empty
        if (s.equals("")) {
            return "-1";
        }

        return s;
    }

    public static void main(String[] args) {
        String s = "avbkjd123klj 456 af";
        System.out.print(extractInt(s)); 
    }
}