CodingGame.java

import java.util.*;
import java.util.stream.Collectors;

public class Main {
    public static void main(String[] args) {
        List<String> matrix = List.of(
                "******c********",
                "*6****o********",
                "******d********",
                "******i********",
                "***********n***",
                "******g********",
                "*9****g*a******",
                "***************",
                "******m********",
                "******e********");

        String result = matrix.stream()
                .map(s -> extract(s))
                .collect(Collectors.joining());
        System.out.println();
    }

    private static String extract(String s){
        if (s==null) return "";
        return Arrays.stream(s.split(""))
                .filter(s1 ->  s1.charAt(0)>96 && s1.charAt(0)<123 )
                .collect(Collectors.joining());
    }
}