可以“这个”在Java中永远是空的？ [英] Can "this" ever be null in Java?

问题描述

在类方法中看到这一行，我的第一反应是嘲笑编写它的开发人员..但是，我想我应该确保我是第一个。

Saw this line in a class method and my first reaction was to ridicule the developer that wrote it.. But then, I figured I should make sure I was right first.

public void dataViewActivated(DataViewEvent e) {
    if (this != null)
        // Do some work
}

该行是否会评估为假？

Will that line ever evaluate to false?

推荐答案

不，不能。如果你正在使用这个，那么你在实例中所以这个不是空的。

No it can't. If you're using this, then you're in the instance so this isn't null.

JLS说：

当用作主表达式时，关键字this表示a value是对调用实例方法的对象（第15.12节）或对正在构造的对象的引用。

When used as a primary expression, the keyword this denotes a value that is a reference to the object for which the instance method was invoked (§15.12), or to the object being constructed.

如果你从一个对象调用一个方法，那么该对象就存在了，或者你之前会有一个 NullPointerException （或者它是一个静态方法但是你不能使用此 in。）

If you invoked a method from an object, then the object exists or you would have a NullPointerException before (or it's a static method but then, you can't use this in it).

资源：

• JLS - 此关键字

• JLS - this keyword

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