表现层-业务层-持久层（模拟依赖关系）

package com.example.service.ui;

import com.example.service.IAccountService;
import com.example.service.impl.AccountServiceImpl;

/**
 * 模拟一个表现层，用于调用业务层
 */
public class Client {
    public static void main(String[] args) {
        IAccountService as=new AccountServiceImpl();
        as.saveAccount();
    }
}

package com.example.service;

/**
 * 账户业务层接口
 */
public interface IAccountService {

    /**
     * 模拟保存账户
     */
    void saveAccount();
}

package com.example.service.impl;

import com.example.service.IAccountService;
import com.example.service.dao.IAccountDao;
import com.example.service.dao.impl.AccountDaoImpl;

/**
 * 账户的业务层实现类
 */
public class AccountServiceImpl implements IAccountService {

    private IAccountDao accountDao=new AccountDaoImpl();

    @Override
    public void saveAccount() {
        accountDao.saveAccount();
    }
}

package com.example.service.dao;

/**
 * 账户的持久层接口
 */
public interface IAccountDao {

    /**
     * 模拟保存账户
     */
    void saveAccount();
}

package com.example.service.dao.impl;

import com.example.service.dao.IAccountDao;

/**
 * 账户的持久层实现类
 */
public class AccountDaoImpl implements IAccountDao {
    @Override
    public void saveAccount(){
        System.out.println("保存了账户");
    }
}