SAP Junior Developer - Cloud Analytics interview questions

I applied through a University job fair and was invited for an in-person interviews at their office in Vancouver. First, I had to do a JavaScript code review and then a coding question. Then the interviewers switched and I had to solve an other coding question and answer OOP questions. The first two interviewers were really friendly but one of the second two guys was quite unfriendly and just stared at me the whole time. The first programming question was easy but the second was actually not so easy and I struggled a bit to solve it. That was also the question where the one interviewer was quite unsupportive. I think I failed the interviewer in the end, because when the unfriendly interviewer asked me for the difference between "interface" and "abstract class", I simply answered "I don't know".