As you know the private classes in Kotlin change to package-private under the hood and internals changed to the public. unfortunately, this can lead to the known problem here.
if the compiler sees the usage of Kotlin internal classes when it wants to change it to the byte code, it can choose package-private for internal kotlin classes that didn't use outside of the package and choose public for others, so we can handle above problem on our own.
Or they can define another annotation such as @JvmPackagePrivate before internal classes to tell the compiler we want a package-private class in java.
Or they can do both.
The question is, why they don't solve this obvious problem with such an obvious solution?
Are they have another approach to solve this?
I just got acquainted with the Kotlin, so I think that I cant create lib for java with kotlin because when I create internal concrete classes, all client can see them outside of the library and its serious problem with kotlin. why they can't see this obvious problem??????
I want to mention that none of the answers in here solve this problem because of @JvmSynthetic and @JvmName just target the fun in kotlin, not classes and at the end they both visible even if they change the name of classes.
at last kotlin claims that it is completely interoperable with java but I think it's not right. better to say that it is 99 percent interoperable with java :)