When should I use File.separator and when File.pathSeparator?

If you mean File.separator and File.pathSeparator then:

• File.pathSeparator is used to separate individual file paths in a list of file paths. Consider on windows, the PATH environment variable. You use a ; to separate the file paths so on Windows File.pathSeparator would be ;.

• File.separator is either / or \ that is used to split up the path to a specific file. For example on Windows it is \ or C:\Documents\Test