Java程序辅导

C C++ Java Python Processing编程在线培训 程序编写 软件开发 视频讲解

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Classes in a hierarchy are related by the is-a relationship.For example, a Nissan is-a Automobile, and a Sentra is-a Nissan.This chapter discusses how reference variablesare used for objects from different classes within a hierarchy.Another subject is the idea of an abstract class — a classthat cannot be instantiated but that can be the parent ofother classes.

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QUESTION 1:

How many Valentine cards did you get this year?