Kotlin-以派生类型访问伴侣对象成员

问题描述

给出以下代码:

open class Foo {
    companion object {
        fun fez() {}
    }
}

class Bar : Foo() {
    companion object {
        fun baz() { fez() }
    }
}

• baz()可以呼叫fez()
• 我可以打电话给Foo.fez()
• 我可以打电话给Bar.baz()
• 但是，我无法拨打Bar.fez()
• baz() can call fez()
• I can call Foo.fez()
• I can call Bar.baz()
• But, I cannot call Bar.fez()

我如何实现最终的行为?

How do I achieve the final behaviour?

推荐答案

伴随对象是其周围类的静态成员:

A companion object is a static member of its surrounding class:

public class Foo {
   public static final Foo.Companion Companion;

   public static final class Companion {
      public final void fez() {
      }

     //constructors
   }
}

对fez()的调用被编译为:

Foo.Companion.fez();

仅供参考:所示的Java代码显示了Kotlin生成的字节码的表示形式.

FYI: The shown Java code shows a representation of the bytecode generated by Kotlin.

结果，您无法调用Bar.fez()，因为Bar中的Companion对象没有该方法.

As a result, you cannot call Bar.fez() because the Companion object in Bar does not have that method.

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