Kotlin - accessing companion object members in derived types [duplicate]

问题

This question already has answers here:

Kotlin: How can I create a “static” inheritable function? (3 answers)

Closed 2 years ago.

Given the following code:

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

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

• baz() can call fez()
• I can call Foo.fez()
• I can call Bar.baz()
• But, I cannot call Bar.fez()

How do I achieve the final behaviour?

回答1:

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
   }
}

The call to fez() is compiled to :

Foo.Companion.fez();

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

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

来源：https://stackoverflow.com/questions/47296133/kotlin-accessing-companion-object-members-in-derived-types