Java：为什么NullPointerExceptions不是NullReferenceExceptions？ [英] Java: Why aren't NullPointerExceptions called NullReferenceExceptions?

问题描述

这是疏忽吗？或者它与JVM有关吗？

Was this an oversight? Or is it to do with the JVM?

推荐答案

Java确实有指针 - 你无法执行指针运算的指针。

Java does indeed have pointers--pointers on which you cannot perform pointer arithmetic.

来自古老的 JLS ：

Java编程语言中有两种类型：primitive类型（§4.2）和引用类型（§4.3）。相应地，有两种数据值可以存储在变量中，作为参数传递，由方法返回，并在以下操作：原始值（§4.2）和参考值（§4.3）。

There are two kinds of types in the Java programming language: primitive types (§4.2) and reference types (§4.3). There are, correspondingly, two kinds of data values that can be stored in variables, passed as arguments, returned by methods, and operated on: primitive values (§4.2) and reference values (§4.3).

以后：

对象是类实例或数组。

参考值（通常只是引用）是指针指向这些对象，以及一个特殊的空引用，它引用无对象。

The reference values (often just references) are pointers to these objects, and a special null reference, which refers to no object.

（强调他们的）

所以，如果你写的话要解释：

So, to interpret, if you write:

Object myObj = new Object();

然后 myObj 是参考类型，其中包含引用值，它本身是新创建的对象的指针。

then myObj is a reference type which contains a reference value that is itself a pointer to the newly-created Object.

因此，如果您将 myObj 设置为 null ，那么您正在设置参考值（又名指针）到 null 。因此，当取消引用变量时，会合理地抛出NullPointerException。

Thus if you set myObj to null you are setting the reference value (aka pointer) to null. Hence a NullPointerException is reasonably thrown when the variable is dereferenced.

不要担心：此主题已经之前热烈讨论过。

Don't worry: this topic has been heartily debated before.

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