This issue was reported via a nashorn-dev email: http://mail.openjdk.java.net/pipermail/nashorn-dev/2015-June/004784.html

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Hi all,
During digging a little into the bytecode generated by Nasgen, there is a pattern of "new ArrayList(memberCount)", but that member count is 1 more that what is needed, this is not always the case, as it depends on the members.
This doesn't have functional impact, but every single byte counts 
The root cause for Prototype, is that Constructor are included in the total count, but it is not added.

To give example:
NativeArrayBuffer$Prototype:

   {      ArrayList list = new ArrayList(2);
      list.add(AccessorProperty.create("slice", 2, "G$slice", "S$slice"));      $nasgenmap$ = PropertyMap.newMap(list);   }
although the list will contain a single entry, ArrayList was initialized by 2.
This also happens in the ScriptClass, e.g.:
NativeArray:   {      ArrayList list = new ArrayList(2);
      list.add(AccessorProperty.create("length", 6, "length", "length"));      $nasgenmap$ = PropertyMap.newMap(list);   }
But it is fine in, e.g.:
ArrayBufferView:   {      ArrayList list = new ArrayList(4);      list.add(AccessorProperty.create("buffer", 7, "buffer", (MethodHandle)null));      list.add(AccessorProperty.create("byteOffset", 7, "byteOffset", (MethodHandle)null));      list.add(AccessorProperty.create("byteLength", 7, "byteLength", (MethodHandle)null));      list.add(AccessorProperty.create("length", 7, "length", (MethodHandle)null));      $nasgenmap$ = PropertyMap.newMap(list);   }
Thanks,Ahmed