Daily Programmer Challenge #296: https://www.reddit.com/r/dailyprogrammer/comments/5j6ggm/20161219_challenge_296_easy_the_twelve_days_of/

Challenge296.java

package com.tomkel.dailyprogrammer;

import com.sun.deploy.util.StringUtils;

import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class Challenge296 {

    private static class DayOfChristmas {
        int date;
        String ordinal;
        String gift;

        DayOfChristmas(int date, String ordinal, String gift) {
            this.date = date;
            this.ordinal = ordinal;
            this.gift = gift;
        }
    }
    

    private static class DaysOfChristmas extends ArrayList<DayOfChristmas> {

        /**
         * Get a single verse
         * @param dayOfChristmas The current day
         * @return String
         */
        private String getVerse(DayOfChristmas dayOfChristmas) {
            List<String> lines = new ArrayList<>(dayOfChristmas.date + 2);
            lines.add(String.format("On the %s day of Christmas", dayOfChristmas.ordinal));
            lines.add("my true love sent to me");

            lines.addAll(
                    stream().filter(d -> d.date <= dayOfChristmas.date)
                            .sorted((day1, day2) -> Integer.compare(day2.date, day1.date)) // Backwards
                            .map(
                                    d -> String.format(
                                            "%s%s %s",
                                            (d.date == 1 && dayOfChristmas.date > 1) ? "and " : "",
                                            d.date,
                                            d.gift
                                    )
                            )
                            .collect(Collectors.toList())
            );

            return StringUtils.join(lines, "\n");
        }

        /**
         * Get the entire song
         * @return String
         */
        private String getSong() {
            List<String> verses = stream().sorted((i, j) -> Integer.compare(i.date, j.date))
                    .map(this::getVerse)
                    .collect(Collectors.toList());

            return StringUtils.join(verses, "\n\n");
        }
    }

    
    public static void main(String[] args) {

        DaysOfChristmas daysOfChristmas = new DaysOfChristmas() {{
            add(new DayOfChristmas(1, "first", "Partridge in a Pear Tree"));
            add(new DayOfChristmas(2, "second", "Turtle Doves"));
            add(new DayOfChristmas(3, "third", "French Hens"));
            add(new DayOfChristmas(4, "fourth", "Calling Birds"));
            add(new DayOfChristmas(5, "fifth", "Golden Rings"));
            add(new DayOfChristmas(6, "sixth", "Geese a Laying"));
            add(new DayOfChristmas(7, "seventh", "Swans a Swimming"));
            add(new DayOfChristmas(8, "eighth", "Maids a Milking"));
            add(new DayOfChristmas(9, "ninth", "Ladies Dancing"));
            add(new DayOfChristmas(10, "tenth", "Lords a Leaping"));
            add(new DayOfChristmas(11, "eleventh", "Pipers Piping"));
            add(new DayOfChristmas(12, "twelfth", "Drummers Drumming"));
        }};

        System.out.print(daysOfChristmas.getSong());
    }
}