SCJP題庫第055題

11. abstract class Vehicle{public int speed(){return 0;}}

12. class Car extends Vehicle{public int speed(){return 60;}}

13. class RaceCar extends Car{public int speed(){return 150;}}

...

21. RaceCar racer = new RaceCar();

22. Car car = new RaceCar();

23. Vehicle vehicle = new RaceCar();

24. System.out.println(racer.speed() + ", " + car.speed()

25. + ", " + vehicle.speed());

What is the result?

 

 

A. 0, 0, 0

B. 150, 60, 0

C. Compilation fails.

D. 150, 150, 150

E. An exception is thrown at runtime.

 

 

Ans: D

 

解說:

 

speed方法為物件方法，是那個版本(Vehicle、Car、RaceCar)的speed依實際物件型態而定。