Do not use Class.hashCode() in hashCode() method.

Class.hashCode() is inherited from Object class, so it may return
diffent value on different JVM.

Change-Id: I9ac9e2847af73a4e172bfe3a8e17b285ee07ffd3
Signed-off-by: Shigeru Yasuda <s-yasuda@da.jp.nec.com>