Objectives(学习目标学习目标)FTo understand objects and classes(理解对象和类理解对象和类)FTo learn how to declare a class and how to create an object of a class.(学习如何定义类和创建类的对象学习如何定义类和创建类的对象)FTo understand the roles of constructors and use constructors to initialize objects.(理解构造方法扮演的角色，会使用构造方法初始化对象)FTo distinguish between object reference variables and primitive data type variables(区分引用变量和基本数据类型区分引用变量和基本数据类型变量变量)FTo declare private data fields with appropriate get and set methods to make class easy to maintain(声明私有
