Use this link to check out the three bundle options with up to 15 books!
Add one of the most popular programming languages to your coding repertoire with this bundle of books on all things Java from O’Reilly! You’ll get a host of books on this powerful and versatile language, like A Functional Approach to Java, which will bring you up to speed on the essential concepts and practices of the functional programming paradigm. Also included are books that cover other languages relevant to Java devs, like Java to Kotlin, which will help you get up and running on the most popular language for native Android apps. Pay what you want for 15 books in total, and help support Code for America with your purchase!
You can always check out the most recent Humble Bundle offers here and here.