In the sketch code downloaded add the following line at the top of of sketch or with other import statements

1. import java.net.URI;

Ah great thanks.

Most of the time these will be Java classes that can't be found. The easy way to resolve it is to use Google to search on
Java API name_of_unfound_class

If you do that you will get a hit on the Java API documentation for the affected class i.e. UnsupportedEncodingException

The top of the webpage looks like this.

To find the package for this class look at the first panel you will see the line

java.io.UnsupportedEncodingException

put an import statement in front and a ; (semi-colon) behind and add it to the sketch.

In this case you are likely to want other classes in this package so to include all the classes from this package use

import java.io.*;

You might change the previous one to

import java.net.*;

as well.

Ah great thanks very much. Great response!