title: How do I implement Serializable in Kotlin so it also works in Java?
body: <p>I have some code that I've been using for years in Java, but need it in Kotlin (its interfaces extend collections interfaces).  Some classes are serializable.  When I try the obvious, I get "Cannot access 'Serializable': it is internal in kotlin.io":</p>
  
  <pre><code>class Foo(val someField:Int): Serializable {
      companion object {
          private const val serialVersionUID = 20180617104400L
      }
  }
  </code></pre>
  
  <p>So, do I just import java.io.Serializable, or will that cause other issues?</p>