The Java Interface

In this section, we dig into the Hadoop FileSystem class: the API for interacting with one of Hadoop’s filesystems.[30] Although we focus mainly on the HDFS implementation, DistributedFileSystem, in general you should strive to write your code against the FileSystem abstract class, to retain portability across filesystems. This is very useful when testing your program, for example, because you can rapidly run tests using data stored on the local filesystem.