I am currently making an app where I will need to store large amounts of data, between 4000 and 7000 user names and an equal amount of register dates.
How do you recommend me doing it?
I am currently making an app where I will need to store large amounts of data, between 4000 and 7000 user names and an equal amount of register dates.
How do you recommend me doing it?
You want a database of some sort. The DB can be either embedded (runs inside your Java process) or stand-alone (runs as a separate daemon process, either on the same machine or on a different one). With an embedded DB, your app will be much simpler to configure; you'll lose a lot of features, but your use case sounds pretty simple, so I wouldn't worry about that right now.
Also, the DB can be table-oriented (SQL) or not (what's known as NoSQL; I don't like that term, because it's not very descriptive, but I don't have anything better). Any of those would work in your case, but I would recommend an SQL-based DB just because SQL is a skill that every programmer needs.
Based on personal experience, I would tell you to use HSQLDB. Also see: Java Embedded Databases Comparison
You should use a DBMS of course.
Here is a good tutorial for building up an application with a database: http://www.androidhive.info/2011/11/android-sqlite-database-tutorial/