we are supporting two versions of Hadoop viz. 1.0.3 and 2.0-alpha. In such situations couple of times you could hit the issue of incompatible APIs. Now if you need to implement an interface for one of the version how would you go about ? The APIs in the two versions are completely incompatible, so would you drop the idea and start supporting one version ? But that’s a big price to pay, thankfully there are couple of things to your rescue in such cases.