first off you question sounds like "how do I do first class functions in java" historically that answer was "make a class with one method, it's shit suck it" things are better now though.

Prior versions of Java also lack predefined functional interfaces and first-class functions such as filter and map. Java 8 reduces verbosity largely by introducing lambdas and method references to ...

The entry point of a standalone Java application is the main method or function. In the age of Servlets and JSPs, Java’s main function took a backseat to these technologies that were initialized with ...