Can you create a .txt file in a Java program?

I'm creating a database, and I want the program to create a .txt file to store information. The user should be able to add more database categories as time goes on. Does a .txt file used in a Java database need to be create on its own, separate from the program, or can it be created in a directory by the program? And if it can be, how would I go about doing so? What is the syntax in Java? Thank you for any help you can give.