The interface who contains only one abstarct method but can have multiple default and static method is called functional interface. Functional Interface define as @FunctionalInterface <= But ...

Your project needs to have a runtime dependency to any SLF4J implementation, e.g. runtime 'ch.qos.logback:logback-classic:1.3.0-alpha4', to see log messages.

gatherers become an obvious and welcome addition to the Stream API. Java streams model dynamic collections of elements. As the spec says, “A stream is a lazily computed, potentially unbounded ...