为什么我们在Java中使用接口引用类型？ [英] Why do we use Interface reference types in Java?

问题描述

我即将参加我的第一个面向对象编程课程的期末考试，我仍然不了解多态性的概念。

I'm about to take the final exam in my very first object-oriented programming class and I still don't understand something about the concept of polymorphism.

假设我有一个抽象类Vehicle，这个类有一个名为Aircraft的子类。我的问题是，这两个代码有什么不同？

Let's say I have an abstract class "Vehicle" and this class has one subclass named "Aircraft". My question is, what is the different between these two codes ?

Aircraft Jetplane = new Aircraft();

和

Vehicle Jetplane = new Aircraft();

推荐答案

在第二个，然后Jetplane可能是其他任何东西继承自车辆，而不仅仅是飞机。例如，你可以有类似的东西

In the second, then Jetplane could be anything else that inherits from Vehicle, not just an Aircraft. For example, you could have something like

Vehicle veh = null;
if (someCondition)
    veh = new Aircraft();
else
    veh = new Boat();

在第一个样本中无法完成，因为船不是飞机。

That can't be done in the first sample, because a Boat is not an Aircraft.

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