Реализация интерфейса Account Service

interface AccountService {
        /**
         * It finds an account by owner id
         *
         * @param id owner unique identifier
         * @return account or null
         */
        Account findAccountByOwnerId(long id);

        /**
         * It count the number of account with balance > the given value
         *
         * @param value
         * @return the number of accounts
         */
        long countAccountsWithBalanceGreaterThan(long value);
    }

    // Declare and implement your AccountServiceImpl here
    class AccountServiceImpl implements AccountService {

        Account[] accounts;

        public AccountServiceImpl(Account[] accounts) {
            this.accounts = accounts.clone();
        }

        public Account findAccountByOwnerId(long id) {
            for (Account account : accounts) {
                if (account.getId() == id) {
                    return account;
                }
            }
            return null;
        }

        public long countAccountsWithBalanceGreaterThan(long value) {
            long counter = 0;
            for (Account account : accounts) {
                if (account.getBalance() > value) {
                    counter++;
                }
            }
            return counter;
        }
    }

    class Account {

        private long id;
        private long balance;
        private User owner;

        public Account(long id, long balance, User owner) {
            this.id = id;
            this.balance = balance;
            this.owner = owner;
        }

        public long getId() {
            return id;
        }

        public long getBalance() {
            return balance;
        }

        public User getOwner() {
            return owner;
        }
    }

    class User {

        private long id;
        private String firstName;
        private String lastName;

        public User(long id, String firstName, String lastName) {
            this.id = id;
            this.firstName = firstName;
            this.lastName = lastName;
        }

        public long getId() {
            return id;
        }

        public String getFirstName() {
            return firstName;
        }

        public String getLastName() {
            return lastName;
        }
    }