我们可以在null对象上调用任何方法吗？ [英] can we call any method on null object?

问题描述

可能吗？

Object obj=null;

obj.someMethod();

someMethod{/*some code here*/}

推荐答案

您可以在空指针上调用静态方法。在静态方法调用中，指针自然会被完全忽略，但是当（看不到类定义）看起来应该导致NullPointerException正常运行时，它仍然是一种情况。

You can call a static method on a null pointer. The pointer will naturally be completely ignored in a static method call, but it's still a case when something that (without looking at the class definition) seemingly should cause a NullPointerException runs just fine.

class FooObject {
    public static void saySomething() {
        System.out.println("Hi there!");
    }
}

class Main {
    public static void main(String[] args) {
        FooObject foo = null;
        foo.saySomething();
    }
}

但只是为了说清楚 - 不，你可以用空指针调用实例方法。保护程序员不受此限制是将Java等语言与C ++等低级语言区别开来的真正基本保护措施之一。它可以在调用端报告错误，而不是在方法本身内部引起一个莫名其妙的段错误。

But just to make it clear - no, you can't call an instance method with a null pointer. Protecting the programmer against this is one of the really basic protections that set languages like Java apart from "lower level languages" such as C++. It enables the error to be reported at the calling end, instead of it causing an inexplicable segfault/whatnot inside the method itself.

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