Folding in Java

SampleFolding.java

import java.math.BigDecimal;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;

import static java.lang.String.format;
import static java.util.Arrays.asList;

class SampleFolding {

    public static void main(String[] args) {

        Fx2<BigDecimal, String, BigDecimal> addAsBigDecimal = (d, s) -> d.add(new BigDecimal(s));
        Collection<String> stringDecimals = asList("1.00", "2.00", "3.00");
        BigDecimal bigDecimal = Folding.foldLeft(addAsBigDecimal, BigDecimal.ZERO, stringDecimals);

        System.out.println(format("Should be 6.00: %s", bigDecimal));

        Fx2<String, BigDecimal, String> appender = (d, s) -> d.concat(s.toString());
        Collection<BigDecimal> decimals = asList(
                new BigDecimal("1.00"), new BigDecimal("2.00"), new BigDecimal("3.00"));
        String stringRep = Folding.foldRight(appender, "", decimals);

        System.out.println(format("Should be 3.002.001.00: %s", stringRep));
    }

    /**
     * Function with arity of 2
     * @param <I1> type of first input
     * @param <I2> type of second input
     * @param <O> type of output
     */
    @FunctionalInterface
    public interface Fx2<I1, I2, O> {

        /**
         * Execute this function
         * @param inputOne first input
         * @param inputTwo second input
         * @return output of this function
         */
        O apply(I1 inputOne, I2 inputTwo);
    }

    public static class Folding {
        //left associative or start from left
        public static <A, B> A foldLeft(final Fx2<A, ? super B, A> f, final A initial, final Collection<B> bc){
            return bc.stream().reduce(initial, f::apply, (c, d) -> d);
        }

        //right associative or start from right
        public static <A, B> A foldRight(final Fx2<A, B, A> f, final A initial, final Collection<B> bc){
            if(bc.size() == 0) {
                return initial;
            }
            List<B> reversed = new ArrayList<>(bc);
            Collections.reverse(reversed);
            return foldLeft(f, initial, reversed);
        }
    }
}