Functional Programming Techniques: Functional Interfaces, Streams, Parallel Collections - Java - page 338

Using Lambda Predefined Interfaces Instead of Your Own

Problem

You want to use existing interfaces, instead of defining your own, for use with Lambdas.

Solution

Use the Java 8 lambda Functional interfaces from java.util.function .

Discussion

In Using Lambdas/Closures Instead of Inner Classes , we used the interface method ac-
ceptCamera() defined in the interface CameraAcceptor . Acceptor-type methods are quite
common, so the package java.util.function includes the Predicate<T> interface, which
we can use instead of CameraAcceptor . This interface has only one method— boolean
test(T t) :

interface interface Predicate Predicate < T > {

boolean

boolean test ( T t );

}

This package includes about 50 of the most commonly needed functional interfaces, such as
IntUnaryOperator , which takes one int argument and returns an int value; LongPredic-
ate , which takes one long and returns boolean ; and so on.