In my GWT-Platform application I have implemented method in which one step is to fetch data from server and next step is dependent on it. I want to prevent my method for further execution of the code until the Async call completes.
Should be something simple but I am not finding a way.
I think you are missing the point about the web being asynchronous.
It is not considered good practice (it is rather an anti-pattern) to block the execution of your client side code until the async call is finished.
So instead of blocking the execution until your async code is finished do following: