Minecolonies – Clean up compiler warnings and type system issues

Minecolonies has a sophisticated requesting system, where you can ask for any ingame material and it will will do all the heavy lifting, all the routing and finding the things to be done in your colony so your request can be fulfilled.

This system relies a lot on java generics to make it as general as possible. But generics in java are limited by what the compiler understands and conversions are not always easy. For example a List<Apple> can't be cast to List<Fruit> as you can't add an Orange to it.

So we used raw types in many places to speed up development. But raw types are not something you want to keep everywhere: https://stackoverflow.com/questions/2770321/what-is-a-raw-type-and-why-shouldnt-we-use-it

When compiling we had many warnings on type safety:

After two pull requests and a combined 100 files touched, compiling goes through with no errors:

Most changes were pretty simple and repetitive: Check what invariants should never be violated by parameters and return types and find the best bound for each type invariant. Then check if code depends on it and do the same there, till all errors are resolved. Then go to the next warning.

Some warnings have to be deliberately suppressed, as the java compiler can be easily confused sometimes and we have to verify by hand that all invariants hold.

I also introduced a few new utility methods to make using the system easier, as there are still a few places where you have to cast. One such method is getRequestOfType:

Previously you had to check for each request if it actually is a Deliverable or a Retryable when you only wanted to handle these. With the Optional pattern, callers don't need any instanceof and casting.

This code only wants to act when the request is of a certain type. And optional makes this really easy with conditionally executing a lambda (or skipping it). And since we say what type we want, no casting is needed.

(The second pull request will be merged in the next couple hours, already got some approval: https://github.com/Minecolonies/minecolonies/pull/1726)

Since this is a fairly technical pull request, the explanation is fairly technical too. If you have any aditional questions, I will answer them in the comments.

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Posted on Utopian.io - Rewarding Open Source Contributors

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