'ant run' failed for java sample code

[ShulinChen]

Hi, I have followed the steps specified in README and successfully built the project, however when it comes to last step 'ant run,' it gives me this following error:

Error: Could not find or load main class "com.tableausoftware.documentation.api.rest.Demo"

Here is the screenshot. It could be awesome if you can help me find out what's wrong.