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!
| Reference: | Java 8 functional interfaces – random musings implementing a Scala type from our JCG partner Biju Kunjummen at the all and sundry blog. |
