如何比较类和接口？

Question

谁能解释我如何比较KClasses 和它们之间的接口？我知道如何检查类或接口是否相等，但我不明白如何检查 A 类是否是 B 类的超类等。

interface IB {}
interface IC : IB {}

open class A {}
open class B : A() {}
open class C : B(), IC {}

fun main(args: Array<String>) {
  if (B::class == B::class) { println("B class is equal to B class") }
  if (IB::class == IB::class) { println("IB interface is equal to IB interface") }
    
  if (A::class ??? B::class) { println("A class is parent of B class") }
  if (A::class ??? C::class) { println("A class is superclass of C class") }
    
  if (C::class ??? IC) { println("C class implements IC interface") }
  if (IC ??? IB) { println("IC interface implements IB interface") }
}

Answer 1

Kotlin 反射没有用于检索 KClass 层次结构信息的 API，因此检查一个 KClass 是另一个 KClass 的超类还是子类的唯一方法是比较相应的 java 类：

interface IB {}
interface IC : IB {}

open class A {}
open class B : A() {}
open class C : B(), IC {}

fun main(args: Array<String>) {
  if (B::class == B::class) { println("B class is equal to B class") }
  if (IB::class == IB::class) { println("IB interface is equal to IB interface") }

  if (A::class.java.isAssignableFrom(B::class.java)) { println("A class is parent of B class") }
  if (A::class.java.isAssignableFrom(C::class.java)) { println("A class is superclass of C class") }

  if (IC::class.java.isAssignableFrom(C::class.java)) { println("C class implements IC interface") }
  if (IB::class.java.isAssignableFrom(IC::class.java)) { println("IC interface implements IB interface") }
}

更新： 您还可以定义两个扩展函数，让这种检查更好一点：

inline fun <reified L : Any, reified R : Any> isSubClassOf(): Boolean {
  return R::class.java.isAssignableFrom(L::class.java)
}

inline fun <reified L : Any, reified R : Any> isSuperClassOf(): Boolean {
  return L::class.java.isAssignableFrom(R::class.java)
}

fun main(args: Array<String>) {
  if (isSubClassOf<B, B>()) { println("B class is equal to B class") }
  if (isSubClassOf<IB, IB>()) { println("IB interface is equal to IB interface") }

  if (isSuperClassOf<A, B>()) { println("A class is parent of B class") }
  if (isSuperClassOf<A, C>()) { println("A class is superclass of C class") }

  if (isSubClassOf<C, IC>()) { println("C class implements IC interface") }
  if (isSubClassOf<IC, IB>()) { println("IC interface implements IB interface") }
}