For all those who love to program in Java and want a Java API for Alpaca, look no further! You can find it here: https://github.com/mainstringargs/alpaca-java.
If you want to backtest your strategies in Java using Polygon Data, I’m currently working on a project available here: https://github.com/Petersoj/AlpacaJavaBacktest. Feel free to contribute!
I’m am also currently working on a momentum based strategy for the Alpaca Java API.