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copied!<p>You're making your own life hard. </p> <pre><code>List<List<Integer>> listOfListOfIntegersBefore = new FunctionArrayList<>(); [...] ((FunctionArrayList<Integer>) listOfIntegersBefore).apply </code></pre> <p>Why not store it as a <code>FunctionArrayList</code> in the first place? Of course you have to cast it this way.</p> <p>Anyway, I find wrapping each list in a functional list a bit annoying, and I'd rather do it with simple static methods: </p> <pre><code>public interface F<S, T> { T apply(S s); } public final class FunctionalStuff { private FunctionalStuff() {} public <S, T> static List<T> map(Collection<? extends S> collection, F<? super S, ? extends T> func) { final List<T> result = new ArrayList<T>(collection.size()); for (S source : collection) result.add(func.apply(source)); return result; } public <S, T> static List<S> filter(Collection<? extends S> collection, F<? super S, Boolean> predicate) { final List<T> result = new ArrayList<T>(collection.size()); for (S source : collection) if (predicate.apply(source)) result.add(source); return result; } // etc etc. } </code></pre> <p>Anyways, please note: I don't advise you to do functional style coding in Java. Wait for closures which will be added in Java 8.</p> <p>Alternatively use a language that embraces functional style: Scala, Javascript, Clojure, Lisp, Mathematica, etc etc, there's a ton of them! Even c(++) seems less annoying at this than Java.</p>

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