对象是否封装数据，以便即使是同一类的其他实例也无法访问数据？ [英] Do objects encapsulate data so that not even other instances of the same class can access the data?

问题描述

在Java中，

对象是否封装数据，以便即使是同一类的其他实例也无法访问数据？只有在使用关键字private时？什么是Java中的访问器方法 - 像getName（）这样的方法？

Do objects encapsulate data so that not even other instances of the same class can access the data? Only when the keyword "private" is used? What are "accessor methods" in Java - methods like getName()?

谢谢

推荐答案

我不倾向于用一个对象来访问另一个对象，而是代码可以访问其中的哪些数据对象。

I don't tend to think of it in terms of one object having access to another, but rather what code has access to what data within an object.

在Java（和C＃，btw）中，类中的代码可以访问同一类的任何对象的私有成员。然后你就拥有了程序包/程序集访问权限和公共访问权限。

In Java (and C#, btw) code within a class has access to the private members of any object of the same class. Then you've got package/assembly access and public access.

棘手的是受保护的访问，这是对的访问代码子类 - 但它取决于目标对象：只允许访问对象的受保护成员，如果它是与代码位置相同类型的实例，或某些子类 - 即使它是暴露由父类。例如，假设你有：

The tricky one is protected access, which is sort of access to code in subclasses - but it depends on the target object: you're only allowed to access protected members of an object if it's an instance of the same type as the location of the code, or some subclass - even if it's being exposed by a parent class. So for instance, suppose you had:

class Parent
{
    protected int x;
}

class Child1 extends Parent
class Child2 extends Parent
class Grandchild extends Child1

然后在 Child1 代码中，您可以访问 Parent.x 仅适用于已知（在编译时）为 Child1 或孙子的实例的对象。例如，您不能使用 new Parent（）。x 或 new Child2（）。x 。

Then within the Child1 code, you can access Parent.x only for objects which are known (at compile-time) to be instances of Child1 or Grandchild. You couldn't, for instance, use new Parent().x or new Child2().x.

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