Как матчить список?

package com.javarush.task.task19.task1908;

/*
Выделяем числа
*/

import java.io.*;
import java.util.ArrayList;

public class Solution {
    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String a = reader.readLine();
//        String b = reader.readLine();
        FileReader fileReader = new FileReader(a);
//        FileWriter fileWriter = new FileWriter(b);
        BufferedReader readerFile = new BufferedReader(fileReader);
//        BufferedWriter writeFile = new BufferedWriter(fileWriter);
        ArrayList<String> list = new ArrayList<>();
        while (readerFile.ready()) {
            list.add(readerFile.readLine());
        }
        for (int i = 0; i < list.size(); i++) {
//            System.out.println(list.get(i));
            if (list.get(i).matches("\\d"))
                System.out.println(list.get(i));
        }
    }
}