分析讲义中Animal类、Dog类、Cat类的关系，使用Animal类声明对象，分别引用不同的子类对象，调用方法，观察结果。总结父类和子类对象的转换

该如何应用

-Analysis of the Animal class lectures, Dog Class, Cat class relations, a statement object using the Animal class, respectively, in different sub-class object reference, call the method, observations. Summarize the parent class and child class object to the conversion of the application