如何访问子类中的方法 [英] How can I access methods in a subclass

问题描述

我目前正在学习 Java，但确实遇到了一些困难.所以我有一个带有子类CD"、游戏"和DVD"的磁盘"类.我有一个数据库"类，它在数组列表中创建磁盘、游戏和 cd 的新实例.数组列表初始化如下:

I am currently learning Java and I'm really struggling with something. So I have a Class "Disk" with the subclasses "CD","Game", and "DVD". I have a "database" class which creates new instances of disk,game and cd in an array list. The array list is initialised like so:

private ArrayList<Disk> disks = new ArrayList(); 

然后我将一个 Game 实例添加到数组中:

I then add an instance of Game to the array:

disks.add(new Game(1999,"SuperGame!",900,"xbox","ea"));

我正在尝试使用以下代码访问游戏子类中的getConsole"方法:

I'm trying to access a method, "getConsole" in the Game subclass using the following code:

Disk currentDisk = disks.get(3);
currentDisk.getConsole();

它说 getConsole 方法不存在.我可以看到问题在于它只访问 Disk 类的方法和字段，但是我如何才能使它可以访问它定义为的子类的方法.感谢您的时间:)

It says the getConsole method doesn't exist. I can see the problem is that it's only accessing the Disk class' methods and fields but how can I make it so it can access the methods of the subclass that it is defined as. Thanks for your time :)

推荐答案

由于 getConsole() 仅在 Game 子类上可用，您需要告诉 Java 您知道您正在查看游戏，并明确地进行转换:

Since getConsole() is available only on the Game subclass, you need to tell Java that you know you're looking at a Game, and cast explicitly:

Disk currentDisk = disks.get(3);
if (currentDisk instanceof Game) {
    ((Game)currentDisk).getConsole();
}

这不是在 Java 中做事的好方法，因为您正在显式测试子类的类型.

This is not a very good way to do things in Java, because you are explicitly testing for the type of subclass.

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