Попробовал на файлах не работает почему то. Объясните плиз.

public class Solution {
    public static String firstFileName;
    public static String secondFileName;
    public static volatile BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));

    static {
        try {
            firstFileName = reader.readLine();
            secondFileName= reader.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }

    }
    //напишите тут ваш код


    public static void main(String[] args) throws InterruptedException {
        systemOutPrintln(firstFileName);
        systemOutPrintln(secondFileName);
    }

    public static void systemOutPrintln(String fileName) throws InterruptedException {
        ReadFileInterface f = new ReadFileThread();
        f.setFileName(fileName);
        f.start();
        f.join();
        System.out.println(f.getFileContent());

    }

    public interface ReadFileInterface {

        void setFileName(String fullFileName);

        String getFileContent();

        void join() throws InterruptedException;

        void start();
    }
    public static class ReadFileThread extends Thread implements ReadFileInterface{
        String fileName;
        String s = "";
        @Override
        public void setFileName(String fullFileName) {
            this.fileName = fullFileName;
        }

        @Override
        public void run() {

            try{
                Scanner scanner = new Scanner(new FileReader(fileName));
                while (scanner.hasNext()) {
                    s += scanner.nextLine()+" ";
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            }
        }

        @Override
        public String getFileContent() {
            return s;
        }

    }


}

static {
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(System.in))) {
            firstFileName = reader.readLine();
            secondFileName = reader.readLine();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }