使用JAVA编程语言实现PIM微型日期管理系统，对初学者的帮助很大。(This assignment involves the creation of simple Personal Information Management system that can deal with 4 kinds of items: todo items, notes, appointments and contacts. Each of these kinds of items is described in more detail below. The assignment requires that you create a class for each item type, and that each class extends an abstract base class provided for you. In addition to creating the four classes, you need to create a manager class that supports some simple text-based commands for creating and managing items.)