What do you want to do?
This is a hard question and your answer can have a lot of interpretations. Be sincere and tell the interviewer exactly what you want to do. You read the job description; therefore, you know that you want this job. Explain to the interviewer the main reasons behind your decision. For example, you could say, I want to become an excellent Java backend developer and your projects are quite challenging in this area. I want to be part of the team that works on these projects. Or, you could say, I want to be part of a major start-up in an important company and this looks like a great opportunity for me. I heard that a new team is being formed and I would be very excited to be part of it. Don't omit saying something about working in a great team! Most probably, you won't be working alone, and being a team player is a major aspect of working in almost any company.