Is there any method which generate random numbers with complexity O(1)

I am looking for one efficent way to generate random numbers using java . I want it to be fast and highly secured. Unfortunately SecureRandom class in java and its method nextBytes() generate highly secured random numbers but this method takes me quite time . I am looking if there is any implementation of a method with the same aim as the one above which has complexity O(1) or worst case O(n).