animal强制转换成Cat类，这个是老师举的一个错误的例子。为什么会报错呢？是因为Cat跟animal不相配，没先把cat对象自动转换成animal，解决方法:在cat强制转换上一行加上“Ainmal ainmal = cat;”并且别忘了先创建cat对象“”

你创建Cat这个类了么

another sample: //char < float;char < double;float < double

float f1 = 1.5f;

double d1= f1;

float f2 =(float) d1; //safe , system will not report error.

char c1= (char) d1; // error, coz the result is not expected

you can add bellowing:  //reason the ture for animal stands for the reference variable which means that it 's a way to point to the created Dog objective

Cat cat = new Cat(); // create a new cat type objective

Animal animal2 = cat; // assign the reference to a big type named animal2

Cat cat = (Cat) animal2; // cut down the extend length