静态方法无法访问类的实例成员 [英] Static method cannot access instance members of a class

问题描述

在Liang的第9版 Java编程简介中，它指出：静态方法无法访问类的实例成员（第312页）。我知道为什么类的实例成员需要访问方法（可能是静态的），但是为什么方法需要访问实例成员？对我来说，访问是指通过点运算符进行访问。换句话说：

In Liang's 9th edition Introduction to Java Programming it states, "A static method cannot access instance members of a class," (pg 312). I see why an instance member of a class would need to access a method (which might be static), but why would a method need to access an instance member? To me, "access" means "access by way of the dot operator." In other words:

 Class myClass = new Class();
 myClass.someStaticMethod();

很有道理，而：

 someNonStaticMethod.myClass

或

 someStaticMethod.myClass

不会。是否允许someNonStaticMethod.myClass语法？我相信我从未见过这种格式。如果不允许，为什么要提到静态方法不能访问类的实例成员？

does not. Is the someNonStaticMethod.myClass syntax allowed? I don't believe I've ever seen such formatting. If it is not allowed, why mention that static methods cannot access instance members of a class?

请帮助解除我的困惑。

-DI

推荐答案

访问实例成员意味着访问实例的字段或属性，而不是实例本身，因为它无法编译。点实际上并不意味着以您的正确思维方式进行访问，我想这就是您感到困惑的根源。点用于在特定对象上调用方法（请参见链接）或访问对象的字段（如果该字段是静态的，则访问类）。

Accessing an instance member means accessing a field or attribute of the instance, not the instance itself since that would not compile. A dot does not literally mean "accessing" in the exact way you think and I guess that's the source of confusion you have. The dot is used to call a method on a certain object (see this link) or to access a field of an object (or class if the field is static).

例如，假设该类的定义如下：

For example, assuming the class is defined as follows:

class MyClass {

   private int x;

   static void foo() {
      ... // foo cannot access member x
   }
}

因此在方法 foo 中，您不能引用 x ，因为它是 MyClass 的成员字段，绑定到 MyClass instance $ c>。

So in method foo, you can't reference x because it is a member field of MyClass that is bound to an instance of MyClass.

另请参见了解类成员，以了解静态成员和实例成员之间的区别。

Also see Understanding Class Members to understand the difference between static members and instance members.

这篇关于静态方法无法访问类的实例成员的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！