静态方法可以访问非静态实例变量吗? [英] Can static method access non-static instance variable?

问题描述

所以我的理解是您不能使用静态方法来访问非静态变量，但是我遇到了以下代码.

So my understanding was that you can't use static method to access non-static variables, but I came across following code.

class Laptop {
  String memory = "1GB";
}
class Workshop {
  public static void main(String args[]) {
    Laptop life = new Laptop();
    repair(life);
    System.out.println(life.memory);
    }
  public static void repair(Laptop laptop) {
    laptop.memory = "2GB";
  }
}

哪个编译没有错误.

不是

public static void repair(Laptop laptop) {
laptop.memory = "2GB";
}

访问类Laptop中定义的字符串内存，这是非静态实例变量吗?

accessing String memory defined in class Laptop, which is non-static instance variable?

由于代码编译时没有任何错误，因此我假设我对这里的内容不了解.有人可以告诉我我不明白的地方吗?

Since the code compiles without any error, I'm assuming I'm not understanding something here. Can someone please tell me what I'm not understanding?

推荐答案

静态方法可以访问其知道的任何实例的非静态方法和字段.但是，如果不知道要在哪个实例上运行，它就不能访问任何非静态的东西.

A static method can access non-static methods and fields of any instance it knows of. However, it cannot access anything non-static if it doesn't know which instance to operate on.

我认为您会误以为这样的例子不起作用:

I think you're mistaking by examples like this that don't work:

class Test {
  int x;

  public static doSthStatically() {
    x = 0; //doesn't work!
  }
}

此处，静态方法不知道应访问哪个 Test 实例.相反，如果它是一种非静态方法，则它将知道 x 引用了 this.x (此处隐含了 this )，但是此在静态上下文中不存在.

Here the static method doesn't know which instance of Test it should access. In contrast, if it were a non-static method it would know that x refers to this.x (the this is implicit here) but this doesn't exist in a static context.

但是，如果您提供对实例的访问权限，即使静态方法也可以访问 x .

If, however, you provide access to an instance even a static method can access x.

示例:

class Test {
  int x;
  static Test globalInstance = new Test();

  public static doSthStatically( Test paramInstance ) {
    paramInstance.x = 0; //a specific instance to Test is passed as a parameter
    globalInstance.x = 0; //globalInstance is a static reference to a specific instance of Test

    Test localInstance = new Test();
    localInstance.x = 0; //a specific local instance is used
  }
}

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