How do I use Processing to read and write data to an Arduino

Processing Electronics (Arduino, etc.)
10 
String s = "foo";
s = "bar";

The String itself is a static object, but the variable can be reassigned to a new String.

Or, methods on the String don’t change the String, they return a new String – which you assign to the reference.

s = s.replace('r', 'z');  // bar -> baz