FactoryMethod

package FactoryMethod;

import java.util.List;

public abstract class Encryptor {
    private SecretKey key;

    public Encryptor(){
        key=createKey();
    }
    public byte[] encryptor(List<String> lines){
        int lengths=0;
        for(String line:lines){
            lengths+=line.length();
        }
        byte[] result=new byte[lengths];
        int i=0;
        for(String line:lines){
            byte[] ct=key.encrypt(line.getBytes());
            for(byte b:ct){
                result[i++]=b;
            }
        }
        return result;
    }
    public abstract SecretKey createKey();
}

class InsecureEncryptor extends Encryptor{
//    private ShortSecretKey key;
    @Override
    public SecretKey createKey() {
        return new ShortSecretKey();
    }
}

import java.nio.charset.StandardCharsets;

public abstract class SecretKey {
    private byte[] key;
    public SecretKey(int n){
        key=new byte[n];
    }
    public byte[] encrypt(byte[] message){
        int m=message.length;
        int k = key.length;
        int j =0;
        byte[] result=new byte[m];
        for(int i=0;i<m;i++){
            result[i] =(byte) (message[i]^key[j]%key.length);
            j+=1;
            if(j==k){
                j=0;
            }
        }
        return result;
    }
    public String decrypt(byte[] message){
        return new String(encrypt(message),StandardCharsets.UTF_8);
    }

}

public class ShortSecretKey extends SecretKey{

    private static final int MAX_LEN=16;
    public ShortSecretKey(){
        super(MAX_LEN);
    }


}