DAO (Data Access Objects) 数据访问对象是第一个面向对象的接口，使用dao设计模式可以方便地对数据进行增删改查，该例对于初学者掌握dao设计模式非常有用-DAO (Data Access Objects) data access object is the first object-oriented interface, use the dao design pattern can easily search for data additions and deletions ，the cases of design patterns is very useful for beginners to master useful dao