Mi código JavaScript:

 var foo = new Foo();

Mi código Java:

 v8Runtime.registerJavaMethod(JavaCallback { _, _ -> Foo("Loan") }, "Foo")

Información de excepción:

 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.loasan.testj2v8/com.loasan.testj2v8.MainActivity}: undefined:32: Unknown return type: class com.loasan.testj2v8.Engine$Foo var foo = new Foo() ^ com.eclipsesource.v8.V8ScriptExecutionException at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3725) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3893) at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140) at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2342) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:269)