关于类型转换异常，类别要分开创建

public class Initial {

public static void main(String[] args) {
    // TODO Auto-generated method stub
    try{
        Animal a1=new Dog();
        Animal a2=new Cat();
        Dog d1=(Dog)a1;
        Dog d2=(Dog)a2;
    }catch(Exception e){
        e.printStackTrace();
        System.out.println("類型轉換異常出現了！");
        System.out.println("Dog d2=(Dog)a2，Cat類不能轉換為Dog！");
    }
}

}