import java.util.regex.Pattern;
import java.util.regex.Matcher;
public class Main {
public static void main(String[] args) {
String str = "###Word1 Word2\nWord3\nWord4 Word5 Word6\n##Word7\n#Word8 Word9\n";
// #+: One or more # characters.
// (.*): Captures everything after the # up to the newline character.
// \n: Matches the newline character.
// Define the regex pattern
String regex = "#+(.*)\n";
// Compile the pattern
Pattern pattern = Pattern.compile(regex);
// Create a matcher to apply the pattern
Matcher matcher = pattern.matcher(str);
// Replace matches with the desired format
str = matcher.replaceAll("_$1_\n");
System.out.println(str);
}
}
/*
run:
_Word1 Word2_
Word3
Word4 Word5 Word6
_Word7_
_Word8 Word9_
*/
