Friend, here is my comment on this question.
There are two ways to develop Android and iOS apps:
1 - Using Frameworks. In this case you can compile the same project for both Android and iOS, see an example of this: Xamarin (which you develop in C # for any device mobile). Or the CoronaLabs . But I do not recommend this solution, besides you get stuck in the framework, you will not have all the flexibility that each platform can offer ... Among other issues, such as performance and memory consumption.
2º - Develop natively. It is the best option and is what the most respected companies do: Android developers and iOS developers. The graphical interface is also available for both, and at the time of implementation the adjustments will be made according to the platform. This is the best way to work on mobile projects.
If you wanted to work productively with iOS, I highly recommend not to try gambiarras, but to get a Mac. For Android, do as you see fit within the flexibility of the platform, ie Linux or Windows.
Speaking sore similarities between languages is complicated, but Objective-C has many peculiarities, just like any other. If you focus on learning, you'll get as much knowledge as Java. But yes, there is a same concept of OOP for both, and that's what matters.
I hope to have helped in some way, conceptually.