Self-learning outside of class is an essential part of Japanese university education. With the drastic changes to university classes due to the COVID-19 pandemic, self-learning became all the more important. In this study, we used surveys to investigate the changes in self-learning from 2019 to 2020, as reported by 5,861 third-year students at 15 universities from June to July 2020. We examined many fields of study and analyzed students' responses based on their learning habits in high school and university, employment, and class type (on-demand, live, and hybrid). The results showed that differences in self-learning habits were reinforced between 2019 and 2020. Moreover, the amount of self-learning varied greatly depending on the field of study and type of class. Self-learning was highest in the on-demand, live, and hybrid classes, respectively, among students in the humanities, social sciences, and health sciences etc. Our results suggest the need to consider effective class methods and class types for a given specialization to promote students' self-learning when remote education is required.