Writing data to and reading data from disk files is a common activity for Java programs in many situations. However, file input/output (I/O) is rarely used in the programs created for robots on the platforms we are working with. As such, and given that file I/O is a large and complex topic, it is not going to be covered here. For those who are interested, here are some resources where you can learn more:

File I/O in Java is done with classes available in the java.io package. You can read about it here [1] and many other places on the web. A newer package of I/O classes was released with Java 7 called java.nio.file and you can read the official documentation here [2].