新手提问：lookup和forname有什么不同？

我的code如下：
InitialContext initialContext = new InitialContext();
Object obj = initialContext.lookup("ejb/library/StudentTransSession");
StudentTransSessionHome studentTransSessionHome = (StudentTransSessionHome)
javax.rmi.PortableRemoteObject.narrow(obj,StudentTransSessionHome.class);
这里我想用forName来拿到StudentTransSeesionHome,为什么编译的时候无法通过呢？说无法转换。
StudentTransSessionHome studentTransSessionHome = (StudentTransSessionHome)Class.forName("library.StudentTransSessionHome");