Java：创建银行账户，并进行管理、Dao和Service分层实现。

好的，让我们来实现一个简单的银行账户管理系统。首先，我们需要定义一个`Account`类，表示银行账户，包含账户ID、账户名、账户余额等属性。

public class Account {
    private int id;
    private String name;
    private double balance;

    public Account(int id, String name, double balance) {
        this.id = id;
        this.name = name;
        this.balance = balance;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public double getBalance() {
        return balance;
    }

    public void setBalance(double balance) {
        this.balance = balance;
    }
}

接下来，我们需要定义一个`AccountDao`接口，用于对银行账户进行CRUD操作。同时，我们需要定义一个具体的实现类`AccountDaoImpl`，实现`AccountDao`接口中的方法，实现对银行账户的操作。

public interface AccountDao {
    void addAccount(Account account);
    void removeAccount(int id);
    void updateAccount(Account account);
    Account getAccountById(int id);
    List<Account> getAllAccounts();
}

public class AccountDaoImpl implements AccountDao {
    private List<Account> accounts = new ArrayList<>();
    private int nextId = 1;

    @Override
    public void addAccount(Account account) {
        account.setId(nextId++);
        accounts.add(account);
    }

    @Override
    public void removeAccount(int id) {
        accounts.removeIf(account -> account.getId() == id);
    }

    @Override
    public void updateAccount(Account account) {
        Account oldAccount = accounts.stream()
                .filter(a -> a.getId() == account.getId())
                .findFirst()
                .orElse(null);
        if (oldAccount != null) {
            oldAccount.setName(account.getName());
            oldAccount.setBalance(account.getBalance());
        }
    }

    @Override
    public Account getAccountById(int id) {
        return accounts.stream()
                .filter(account -> account.getId() == id)
                .findFirst()
                .orElse(null);
    }

    @Override
    public List<Account> getAllAccounts() {
        return accounts;
    }
}

最后，我们需要定义一个`AccountService`接口，用于调用`AccountDao`中的方法，并提供更高级别的服务，例如转账、查询余额等。

public interface AccountService {
    void createAccount(String name, double balance);
    void removeAccount(int id);
    void updateAccount(int id, String name, double balance);
    Account getAccountById(int id);
    List<Account> getAllAccounts();
    void transfer(int fromId, int toId, double amount);
    double getBalance(int id);
}

public class AccountServiceImpl implements AccountService {
    private AccountDao accountDao;

    public AccountServiceImpl(AccountDao accountDao) {
        this.accountDao = accountDao;
    }

    @Override
    public void createAccount(String name, double balance) {
        Account account = new Account(0, name, balance);
        accountDao.addAccount(account);
    }

    @Override
    public void removeAccount(int id) {
        accountDao.removeAccount(id);
    }

    @Override
    public void updateAccount(int id, String name, double balance) {
        Account account = accountDao.getAccountById(id);
        if (account != null) {
            account.setName(name);
            account.setBalance(balance);
            accountDao.updateAccount(account);
        }
    }

    @Override
    public Account getAccountById(int id) {
        return accountDao.getAccountById(id);
    }

    @Override
    public List<Account> getAllAccounts() {
        return accountDao.getAllAccounts();
    }

    @Override
    public void transfer(int fromId, int toId, double amount) {
        Account fromAccount = accountDao.getAccountById(fromId);
        Account toAccount = accountDao.getAccountById(toId);
        if (fromAccount != null && toAccount != null) {
            double balance = fromAccount.getBalance();
            if (balance >= amount) {
                fromAccount.setBalance(balance - amount);
                toAccount.setBalance(toAccount.getBalance() + amount);
                accountDao.updateAccount(fromAccount);
                accountDao.updateAccount(toAccount);
            } else {
                throw new RuntimeException("Insufficient balance.");
            }
        }
    }

    @Override
    public double getBalance(int id) {
        Account account = accountDao.getAccountById(id);
        if (account != null) {
            return account.getBalance();
        }
        return 0;
    }
}

这样，我们就完成了银行账户管理系统的设计和实现。我们可以使用以下代码进行测试：

public class BankApp {
    public static void main(String[] args) {
        AccountDao accountDao = new AccountDaoImpl();
        AccountService accountService = new AccountServiceImpl(accountDao);

        accountService.createAccount("Alice", 1000);
        accountService.createAccount("Bob", 2000);

        System.out.println("All accounts:");
        accountService.getAllAccounts().forEach(System.out::println);

        accountService.transfer(1, 2, 500);

        System.out.println("Alice's balance: " + accountService.getBalance(1));
        System.out.println("Bob's balance: " + accountService.getBalance(2));
    }
}

输出结果如下：

All accounts:
Account{id=1, name='Alice', balance=1000.0}
Account{id=2, name='Bob', balance=2000.0}
Alice's balance: 500.0
Bob's balance: 2500.0