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by Jeff Heon.
Original Post: A simple Java FP list map
Feed Title: The Careful Programmer
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Feed Description: A (starting) collection of my musings about programming. I'll brush more often on Scala related topics since I am currently learning it.
Following on the comments I received on my previous entry about doing a bit of Java functional programming style, I made a very simple class to map a list. I'm following the style of what I have seen in the apache collections utilities. See previous post.
First note that I am doing it without generics, so for some this would be old style Java programming.
Here's the utility class. ListUtils.java package fp;
public class ListUtils { static public List map(List elements, Applier applier) { List result = new ArrayList(); for (Iterator it = elements.iterator(); it.hasNext();) { Object element = it.next(); result.add(applier.apply(element)); } return result; } }
And the interface used by the utility class. Applier.java package fp;
public interface Applier { public Object apply(Object element); }
Here's a client code example.
WithPoints.java package domino;
public interface WithPoints { public Integer getPoints(); }
Domino.java package domino;
public class Domino implements WithPoints { private Integer points;
public Domino(int points) { this.points = new Integer(points); }
public static void main(String[] args) { List dominoes = new ArrayList(); dominoes.add(new Domino(1)); dominoes.add(new Domino(2)); dominoes.add(new Domino(3));
List points = ListUtils.map(dominoes, new Applier() { public Object apply(Object domino) { return ((WithPoints) domino).getPoints(); } });
System.out.println(points); // [1, 2, 3] } }
So this time around, I did get a new list instead of transforming a list but I still think the simple iterator style is clearer and it avoids using a "utility class" for doing something really simple.
Iterator style List points; for (Iterator iter = Dominoes.iterator(); iter.hasNext();) { points.add((WithPoints) iter.next().getPoints()); }
And of course, Scala still is neater for me 8) val points = dominoes map (x => x.points)
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