第58題

Given:

10. interface Foo{}
11. class Alpha implements Foo{}
12. class Beta extends Alpha{}
13. class Delta extends Beta{
14. public static void main(String[] args){
15. Beta x = new Beta();
16. //insert code here
17. }
18. }
Which code, inserted at line 16, will cause a java.lang.ClassCastException?
A. Alpha a = x;
B. Foo f = (Delta)x;
C. Foo f = (Alpha)x;
D. Beta b = (Beta)(Alpha)x;
答案：B
參考：7-8 物件的轉型

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B. Foo f = (Delta)x; // x 為 Delta 的 父類別 Beta, 父類別不可強制轉型為子類別.