i’m trying to take the user input and double any numbers found by using the split method closed

1. You need a loop to continue the execution until the user inputs EXIT.
2. You can match and replace an integer using a regex.

Demo:

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

public class Main {
    public static void main(String[] args) {
        Scanner kbReader = new Scanner(System.in);
        String userIn;

        Pattern pattern = Pattern.compile("\\b\\d+\\b");// String of one or more digits bounded by word-boundary

        while (true) {
            System.out.print("Please type in a sentence, or type EXIT to end the program: ");
            userIn = kbReader.nextLine();

            if ("EXIT".equalsIgnoreCase(userIn)) {
                break;
            }

            StringBuilder sb = new StringBuilder();
            Matcher matcher = pattern.matcher(userIn);
            int lastProcessedIndex = 0;

            while (matcher.find()) {
                String number = matcher.group();
                int startIndex = matcher.start();

                // Append the string starting from the last processed index and then append the
                // doubled integer
                sb.append(userIn.substring(lastProcessedIndex, startIndex))
                        .append(String.valueOf(2 * Integer.parseInt(number)));

                // Update the last processed index
                lastProcessedIndex = startIndex + number.length();
            }
            // Append the remaining substring
            sb.append(userIn.substring(lastProcessedIndex));

            System.out.println("The updated string: " + sb);
        }
    }
}

A sample run:

Please type in a sentence, or type EXIT to end the program: hello 10 world 5 how are 15 doing?
The updated string: hello 20 world 10 how are 30 doing?
Please type in a sentence, or type EXIT to end the program: exit