亚型多态性与阵列 [英] Subtype polymorphism and arrays

问题描述

Computer[] labComputers = new Computer[10];

与

public class Computer {
...
     void toString(){
     // print computer specs
     }
}
public class Notebook extends Computer{
...
     void toString(){
     // print computer specs + laptop color
     }
}

每个标变量 labComputers [I] 可以引用电脑对象或笔记本电脑对象，因为笔记本电脑是电脑的子类。方法调用 labComputers [I]的ToString（），多态性确保正确的的toString 方法被调用。

each subscripted variable labComputers[i] can reference either a Computer object or a Notebook object because Notebook is a subclass of Computer. For the method call labComputers[i].toString(), polymorphism ensures that the correct toString method is called.

我不知道如果我们做

Notebook[] labComputers = new Notebook[10];

我会得到什么样的或错误的，如果我与电脑对象和笔记本电脑对象

推荐答案

由于这个问题专门询问类型的错误我会跟下面的场景解释它们

Since the question specifically asks about kind of error I will explain them with below scenarios

如果您做以下

Notebook[] labComputers = new Notebook[10];

在阵列现在可以只设置笔记本对象。

Now you can only set Notebook objects in array.

labComputers[0]  = new Notebook(); // Fine
labComputers[1]  = new Computer(); // Compilation error 

现在，如果你做

Computer[] notebooks = new Notebook[10];
notebooks[0] = new Notebook();
notebooks[1] = new Computer(); // <--- ArrayStoreException

由于数组是 covarant ，自然界中的具体化，即。如果子是一个亚型中超，然后数组类型子[] 是的亚型超级[] 和数组强制在运行时它们的元素类型会引起ArrayStoreException信息

Because arrays are covarant,reified in nature ie. if Sub is a subtype of Super, then the array type Sub[] is a subtype of Super[], and arrays enforce their element types at run time it will cause ArrayStoreException

您可以阅读甲骨文的文档有关多态性知道更多的它是如何工作。

You can read oracle docs about Polymorphism to know more how it works.

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