DAO

package com.atguigu.java2;
import java.util.List;
/**
 * @author Dxkstart
 * @create 2021-05-28 10:28
 *
 *
 *DAO：data(base) access object  ---数据访问对象
 *
 */
public class DAO <T>{//操作数据库中所有表的一些通用操作的DAO
    //添加一条记录
    public void add(T t){
    }
    //删除一条记录
    public boolean remove(int index){
        return false;
    }
    //修改一条记录
    public void update(int index,T t){
    }
    //查询一条记录
    public T getIntex(int index){
        return null;
    }
    //查询多条记录
    public List<T> getForList(int index){
        return null;
    }
    //泛型方法
    //举例：获取表中一共有多少条记录？获取最大的员工入职时间？
    public <E> E getValue(){
        return null;
    }
}

package com.atguigu.java2;
import org.junit.Test;
import java.util.List;
/**
 * @author Dxkstart
 * @create 2021-05-28 10:41
 */
public class DAOTest {
    @Test
    public void test1(){
        CustomerDAO dao1 = new CustomerDAO();
        dao1.add(new Customer());
        List<Customer> list = dao1.getForList(10);
        StudentDAO dao2 = new StudentDAO();
        Student student = dao2.getIntex(1);
    }
}

package com.atguigu.java2;
/**
 * @author Dxkstart
 * @create 2021-05-28 10:34
 */
public class Customer {//此类对应数据库中的customers表
}

package com.atguigu.java2;
/**
 * @author Dxkstart
 * @create 2021-05-28 10:36
 */
public class CustomerDAO extends DAO <Customer>{//只能操作Customer表的DAO
}

package com.atguigu.java2;
/**
 * @author Dxkstart
 * @create 2021-05-28 10:45
 */
public class Student {
}

package com.atguigu.java2;
/**
 * @author Dxkstart
 * @create 2021-05-28 10:45
 */
public class StudentDAO extends DAO<Student>{//只能操作Student表的DAO
}