Ребята, помогите пожалуйста. Валидатор каким-то чудом прошел, но непонятки с методом contains.

public class Solution {
    public static List<String> allLines = new ArrayList<String>();
    public static List<String> forRemoveLines = new ArrayList<String>();

    public static void main(String[] args) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        String namefile1 = reader.readLine();
        String namefile2 = reader.readLine();
        BufferedReader readerfile1 = new BufferedReader(new FileReader(namefile1));
        BufferedReader readerfile2 = new BufferedReader(new FileReader(namefile2));

        while (readerfile1.ready()){
            allLines.add(readerfile1.readLine());
        }
        while (readerfile2.ready()){
            forRemoveLines.add(readerfile2.readLine());
        }
        for (int i = 0; i < allLines.size(); i++)
            System.out.println(allLines.get(i));
        for (int i = 0; i < forRemoveLines.size(); i++)
            System.out.println(forRemoveLines.get(i));
        try {
            new Solution().joinData();
        }catch (CorruptedDataException e){
            System.out.println("не содержит");
        }
        reader.close();
        readerfile1.close();
        readerfile2.close();

    }

    public void joinData() throws CorruptedDataException {
        boolean isContain = true;
        for (int i = 0; i < forRemoveLines.size(); i++){
            String str = forRemoveLines.get(i);
            if (!allLines.contains(str)){
                isContain = false;
                break;
            }
        }
        if (isContain){
            for (int i = 0; i < forRemoveLines.size(); i++){
                allLines.remove(forRemoveLines.get(i));
            }
        }
        else {
            allLines.clear();
            throw new CorruptedDataException();
        }

    }
}