object ArrayBuffer
{
  def empty[T](i : Int) = new scala.collection.mutable.ArrayBuffer[T] {
    override val initialSize = i
  }
}

object Test extends Application
{
  val ab = ArrayBuffer.empty(10)
}

java.lang.VerifyError: class ArrayBuffer$$$$anon$$1 overrides final method initialSize.()I
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
        at java.net.URLClassLoader.access$$000(URLClassLoader.java:56)
        at java.net.URLClassLoader$$1.run(URLClassLoader.java:195)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
        at Test$$.<init>(t.scala:10)
        at Test$$.<clinit>(t.scala)
        at Test.main(t.scala)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at scala.tools.nsc.ObjectRunner$$$$anonfun$$run$$1.apply(ObjectRunner.scala:75)
        at scala.tools.nsc.ObjectRunner$$.withContextClassLoader(ObjectRunner.scala:49)
        at scala.tools.nsc.ObjectRunner$$.run(ObjectRunner.scala:74)
        at scala.tools.nsc.MainGenericRunner$$.main(MainGenericRunner.scala:161)
        at scala.tools.nsc.MainGenericRunner.main(MainGenericRunner.scala)

$$ javap -classpath scala-library.jar scala.collection.mutable.ArrayBuffer | grep initial
    public final void initialSize_$$eq(int);
    public final int initialSize();