java - Kotlin noarg 插件 : Constructor only accessible by java reflection

Question

我的设置有问题，但我不知道它是什么。 来自 Kotlin compiler plugins我有以下信息。

The no-arg compiler plugin generates an additional zero-argument constructor for classes with a specific annotation.

The generated constructor is synthetic so it can’t be directly called from Java or Kotlin, but it can be called using reflection.

也就是说，我认为我可以通过 java 和 kotlin 反射访问 noarg 构造函数，但我只能通过 java 反射访问它。这是预期的行为，还是我做错了什么？

构建.gradle

plugins {
    id 'org.jetbrains.kotlin.jvm' version '1.3.50'
    id "org.jetbrains.kotlin.plugin.noarg" version "1.3.50"
    id 'application'
    id 'java'
}

repositories {
    mavenCentral()
    jcenter()
}

dependencies {
    implementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8'
    compile group: 'org.jetbrains.kotlin', name: 'kotlin-reflect', version: '1.3.50'
}

noArg {
    annotation('noargdemo.Entity')
}

application {
    mainClassName = 'noargdemo.AppKt'
}

package noargdemo

import kotlin.reflect.full.createInstance

@Target(AnnotationTarget.CLASS)
@Retention(AnnotationRetention.RUNTIME)
annotation class Entity

@Entity
data class Employee(
        val firstName : String,
        val secondName : String
)

fun main(args: Array<String>) {
    val kotlinConstructors = Employee::class.constructors // size is 1
    val javaConstructors = Employee::class.java.constructors // size is 2
    val instance1 = Employee::class.java.getConstructor().newInstance() // works
    val instance2 = Employee::class.createInstance() // doesnt work
}

Answer 1

这是预期的行为，甚至在您引用的描述中也有说明:

The generated constructor is synthetic so it can’t be directly called from Java or Kotlin, but it can be called using reflection.

合成方法是编译器出于内部目的而生成的方法，无法从源代码手动调用它们，但它们对于反射是可见的。

您可以使用 Method.isSynthetic 检查方法是否是合成的: https://docs.oracle.com/javase/8/docs/api/java/lang/reflect/Method.html#isSynthetic--