Several major companies have been hacked lately. Security advice for web users last week from the US Department of Homeland Security encouraging to disable java on browsers. Disable java in each browser takes time. You will learn how to disable java for all at once. and also for each browser if needed.
This article explain the usage of IntentService class in android SDK to perform background processing to offload tasks from an application’s main thread (Your activity).
when IntentService jobs done, the results are sent back to the activity.
You may reach a point where you need to transfer data from a server (web-service) to a an android client. although, there are many ways to achieve that goal, one of the simplest is using JSON. JSON is better then XML in terms of small bandwidth footprint. it has a lot of libraries for every available platform, so it makes the best solution for server-client communication.