Functional Programming Techniques: Functional Interfaces, Streams, Parallel Collections - Java - page 349

Example 9-3 creates an AutoCloseable for use in a try-with-resource (see Try With Re-
sources ) . The normal AutoCloseable method is close() , but ours is named cloz() . The
AutoCloseable reference variable autoCloseable is created inside the try statement, so its
close-like method will be called when the body completes. In this example, we are in a static
main method wherein we have a reference rnd2 to an instance of the class, so we use this in
referring to the AutoCloseable -compatible method.

Example 9-3. ReferencesDemo2.java
public public class class ReferencesDemo2 ReferencesDemo2 {

void void cloz () {

System . out . println ( "Stand-in close() method called" );

}

public public static static void void main ( String [] args ) throws throws Exception {

ReferencesDemo2 rd2 = new new ReferencesDemo2 ();

// Use a method reference to assign the AutoCloseable interface
// variable "ac" to the matching method signature "c" (obviously
// short for close, but just to she the method name isn't what matters).
try try ( AutoCloseable autoCloseable = rd2: : cloz ) {

System . out . println ( "Some action happening here." );

}

}

}

The output is as follows:

Some action happening here.
Stand-in close() method called

It is, of course, possible to use this with your own functional interfaces, defined as in Creat-
ing Your Own Functional Interfaces . You're also probably at least vaguely aware that any
normal Java object reference can be passed to System.out.println() and you'll get some
description of the referenced object. Example 9-4 explores these two themes. We define a
functional interface imaginatively known as FunInterface with a method with a bunch of
arguments (merely to avoid it being mistaken for any existing functional interface). The
method name is process , but as you now know the name is not important; our implementa-
tion method goes by the name work . The work method is static, so we could not state that the
class implements FunInterface (even if the method names were the same; a static method
may not hide an inherited instance method), but we can nonetheless create a lambda referen-