In Java 8, there are a lot of functional interfaces are introduced in the java.util.function package and the more common ones include but are not limited to:
Function – it takes one argument and returns a result
Consumer – it takes one argument and returns no result (represents a side effect)
Supplier – it takes no argument and returns a result
Predicate – it takes one argument and returns a boolean
BiFunction – it takes two arguments and returns a result
BiConsumer - it takes two (reference type) input arguments and returns no result
BinaryOperator – it is similar to a BiFunction, taking two arguments and returning a result. The two arguments and the result are all of the same types
UnaryOperator – it is similar to a Function, taking a single argument and returning a result of the same type
Runnable: use to execute the instances of a class over another thread with no arguments and no return value.
Callable: use to execute the instances of a class over another thread with no arguments and it either returns a value or throws an exception.
Comparator: use to sort different objects in a user-defined order
Comparable: use to sort objects in the natural sort order
