Stream API, which has been introduced in Java 8, is probably still the most important new feature that has been included to Java during last several years. I think that every Java developer has an opportunity to use Java Stream API in his career. Or I should rather told that you probably use it on a day-to-day basis. However, if you compare the built-in features offered for functional programming with some other languages – for example Kotlin – you will quickly realize that the number of methods provided by Stream API is very limited. Therefore, the community has created several libraries used just for extending API offered by pure Java. Today I’m going to show the most interesting Stream API extensions offered by the three popular Java libraries: StreamEx, jOOλ and Guava.