Classes
类
Classes are the most important building block of any object-oriented system. A class is a description of a set of objects that share the same attributes, operations, relationships, and semantics. A class implements one or more interfaces.
在不论什么的面向对象系统中，类都是最重要的构建模块．类描写叙述一组对象，这组对象共享同样的属性，操作，关系和语义．类实现一个或多个接口．
You use classes to capture the vocabulary of the system you are developing. These classes may include abstractions that are part of the problem domain, as well as classes that make up an implementation. You can use classes to represent software things, hardware things, and even things that are purely conceptual.
使用类捕捉正在开发的系统的词汇．这些类可能包括抽象的问题域部分，以及类组成的实现．你能够使用类表达软件事物，硬件事物，甚至是那些纯概念的事物．
Well-structured classes have crisp boundaries and form a part of a balanced distribution of responsibilities across the system.
具有良好结构的类有着清晰的界限和形成一个跨系统的责任分配均衡的一部分．