How to construct a relative path in Java from two absolute paths (or URLs)?

Question

Given two absolute paths, e.g.

/var/data/stuff/xyz.dat
/var/data

How can one create a relative path that uses the second path as its base?

Answer 1

If you know the second string is part of the first:

String s1 = "/var/data/stuff/xyz.dat";
String s2 = "/var/data";
String s3 = s1.substring(s2.length());

or if you really want the period at the beginning as in your example:

String s3 = ".".concat(s1.substring(s2.length()));