Difference between File.separator and slash in paths

Question

What is the difference between using File.separator and a normal / in a Java Path-String?

In contrast to double backslash \\\\

Answer 1

Well, there are more OS's than Unix and Windows (Portable devices, etc), and Java is known for its portability. The best practice is to use it, so the JVM could determine which one is the best for that OS.