Welcome to Scala version 2.7.1.final (Java HotSpot(TM) 64-Bit Server
VM, Java 1.6.0_01-dp).
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scala> import collection.mutable.ArrayBuffer
import collection.mutable.ArrayBuffer

scala> val ls = new ArrayBuffer[Int]{ override val initialSize = 100 }
java.lang.VerifyError: class $$anon$$1 overrides final method initialSize.()I
       at java.lang.ClassLoader.defineClass1(Native Method)
       at java.lang.ClassLoader.defineClass(ClassLoader.java:675)
       at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
       at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
       at java.net.URLClassLoader.access$$000(URLClassLoader.ja...