Make sure you have either Android Studio or ADT Bundle installed.
My config: Windows 7 + JDK 1.7.0_71 + ADT Bundle 20140702 + Android Studio 2.2 and OSX EI Capitan + (JDK 1.7.0_71 + ADT Bundle 20140702) + (JDK 1.8.0_91 + Android Studio 2.1.2). All the systems and software are 64 bit.
Open an existing Android Studio project > Select the path of APIJSON-Demo-master/APIJSON-Android/APIJSONApp(or APIJSONTest） > OK
Run > Run app
In the browser, send a request to the server. It should return with the result. If the default url is not available, change it to an available one, such as an IPV4 address that is running the server of the APIJSON project. Then click the request button again.