Over a million developers have joined DZone.

Java 8 Functional Interfaces - Random Musings Implementing a Scala Type

· Java Zone

Navigate the Maze of the End-User Experience and pick up this APM Essential guide, brought to you in partnership with CA Technologies

In one of the assignments of the Functional programming with Scala course a type called Terrain is introduced - Terrain represents a region parts of which are accessible and parts which are not. So in a very clever way Terrain is defined the following way in the assignment:

case class Pos(x:Int, y: Int)

type Terrain = Pos => Boolean


Essentially Terrain is a function which takes a position and for that position returns a boolean based on whether the position is accessible or not!

Given this definition of Terrain, a way to define an "infinite" terrain where every position is accessible is done this way:

val infiniteTerrain = (pos: Pos) => true


or another terrain, where certain coordinates are accessible can be defined this way:

def terrainFunction(vector: Vector[Vector[Char]]) : Terrain = {
 (pos: Pos) => {
  if (pos.x > vector.size - 1 || pos.y > vector(0).size - 1 || pos.x < 0 || pos.y < 0) {
   false
  } else {
   val ch = vector(pos.x)(pos.y)
   ch == 'o';
  }
 }
}  

val terrain1 = terrainFunction(Vector(
     Vector('-','-','-'),
     Vector('-','o','-'),
     Vector('-','o','-'),
     Vector('-','o','-'),
     Vector('-','-','-')
     )
    )


All extremely clever.

Now, given that Java 8 release is imminent, an equally(almost :-) ) clever code can be attempted using Java 8 constructs:

whereas the Terrain could be defined as a function signature in Scala, it has to be defined as a functional interface with Java 8:

interface Terrain {
 public boolean isAccessible(Pos pos);
}


Given this interface, an infinite terrain looks like this using Lambdas in Java 8:

Terrain infiniteTerrain = (pos) -> true;


The terrainFunction equivalent in Java 8 can be defined along these lines:

public Terrain terrainFunction(char[][] arr) {
 return (pos) -> {
  if (pos.x > arr.length - 1 || pos.y > arr[0].length - 1 || pos.x < 0 || pos.y < 0) {
   return false;
  } else {
   char ch = arr[pos.x][pos.y];
   return ch == 'o';
  }
 };
}
 
char[][] arr = {
 {'-','-','-'},
 {'-','o','-'},
 {'-','o','-'},
 {'-','o','-'},
 {'-','-','-'}
};
Terrain terrain = terrainFunction(arr); 

assertTrue(terrain.isAccessible(new Pos(1, 1)));

Close enough!

Thrive in the application economy with an APM model that is strategic. Be E.P.I.C. with CA APM.  Brought to you in partnership with CA Technologies.

Topics:

Published at DZone with permission of Biju Kunjummen, DZone MVB. See the original article here.

Opinions expressed by DZone contributors are their own.

The best of DZone straight to your inbox.

SEE AN EXAMPLE
Please provide a valid email address.

Thanks for subscribing!

Awesome! Check your inbox to verify your email so you can start receiving the latest in tech news and resources.
Subscribe

{{ parent.title || parent.header.title}}

{{ parent.tldr }}

{{ parent.urlSource.name }}