Understanding Async Methods in Web Service

I consume Java Service in my .NET appliaction. I have one question: When service serialize in .NET he also create Async methods. For example for GetPersons() method ser开发者_StackOverflow中文版vice create GetPersonsAsync() which is return void. In which cases I can use this Async methods and what the destination of these methods.

Generally, for async methods, you also need to specify a callback method. The called web method immediately returns but keeps working in the backround. When its done, it invokes your callback method with its results