Question

为什么Kotlin不允许创建私有内部类的公共实例，而不像Java？

适用于Java：

public class Test {
  public A a = new A();

  private class A {
  }
}

在Kotlin中不起作用（A类必须是public）：

class Test {
    var a = A()
//      ^  
// 'public' property exposes its private type 'A'

    private inner class A
}

Answer 1

I would assume because there isn't really a case where it seems like the right thing to do. Any code accessing the property a would not have access to its type. You couldn't assign it to a variable. Test.A myVar declaration outside of the Test class would error out. By not allowing it, the code will be forced to be more consistent. A better question would be why would Java allow it? Other languages, such as swift, have the same restriction.

Answer 2

https://kotlinlang.org/docs/reference/visibility-modifiers.html#classes-and-interfaces

陈述：

对Java用户的注意：外部类在Kotlin中看不到其内部类的私有成员。

对于您的用例，您可以使用Nested Classes

在private inner classes中，您只能访问外层成员。

我认为kotlin团队以这种方式实现了它，因此可以将private inner classes中的成员范围缩小到只能在inner class内访问。我认为这在Java中是不可能的。

在Kotlin中创建私有内部类的公共实例

2 个答案: