为什么可以在Java中抛出null？ [英] Why can I throw null in Java?
问题描述
运行时：
public class WhatTheShoot {
public static void main(String args[]){
try {
throw null;
} catch (Exception e){
System.out.println(e instanceof NullPointerException);
System.out.println(e instanceof FileNotFoundException);
}
}
}
响应是： p>
The response is:
true
false
对我来说这是相当惊人的。我会认为这会净化编译时错误。
Which was fairly stunning for me. I would have thought this would net a compile-time error.
为什么我可以在Java中抛出null，为什么会将其上传到NullPointerException？
（实际上，我不知道这是否是一个upcast，因为我抛出null）
除了真正非常愚蠢的面试问题（请不要在面试中问这个问题），我看不出有什么理由来 throw null 。也许你想被解雇，但这是...我的意思是，为什么还有人会将$ code> throw null ？
Aside from a really really stupid interview question (please nobody ask this in an interview) I cannot see any reason to throw null. Maybe you want to be fired, but that's... I mean, why else would anyone throw null?
有趣的事实 IntelliJ IDEA 12告诉我，我的行 e instanceof NullPointerException ，始终为false。这不是真的。
Fun fact IntelliJ IDEA 12 tells me that my line, e instanceof NullPointerException, will always be false. Which isn't true at all.
推荐答案
看起来不是这样的 null 被视为 NullPointerException ，但尝试的行为抛出null 本身抛出一个 NullPointerException 。
It looks like it's not that null is treated as a NullPointerException, but that the act of attempting to throw null itself throws a NullPointerException.
换句话说， throw 检查其参数是否为null，如果为null，则会抛出 NullPointerException 。
In other words, throw checks that its argument is nonnull, and if it is null, it throws a NullPointerException.
JLS 14.18 指定这个行为：
JLS 14.18 specifies this behavior:
表达式正常完成，产生一个空值，然后创建NullPointerException类的实例V'并抛出而不是null。然后，throw语句突然完成，原因是抛出V'值。
If evaluation of the Expression completes normally, producing a null value, then an instance V' of class NullPointerException is created and thrown instead of null. The throw statement then completes abruptly, the reason being a throw with value V'.
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