DeathSavingThrow.java

import java.util.ArrayList;
import java.util.List;

public class Launcher {

    public static void main(String[] args) {
        List<String> rolls = roll();
        if (rolls.contains("error")) {
            System.out.println("ERROR!");
        } else {
            Integer total = rolls.size();
            Integer timesLife = count(rolls, "life");
            Integer timesStable = count(rolls, "stable");
            Integer timesSurvive = timesLife + timesStable;
            Integer timesDeath = count(rolls, "death");

            System.out.println(total + " possibilities.");
            System.out.println(timesLife + " times life, which is " + ((double) timesLife / total) * 100 + " percent");
            System.out.println(timesStable + " times stable, which is " + ((double) timesStable / total) * 100 + " percent");
            System.out.println(timesDeath + " times death, which is " + ((double) timesDeath / total) * 100 + " percent");

            System.out.println();

            System.out.println(timesSurvive + " times survived, which is " + ((double) timesSurvive / total) * 100 + " percent");
        }
    }

    private static List<String> roll() {
        ArrayList<String> result = new ArrayList<>();
        ArrayList<Integer> rolls;

        for (int i = 20; i > 0; i--) {
            rolls = new ArrayList<>();
            rolls.add(i);
            result.addAll(roll(rolls));
        }
        return result;
    }

    private static List<String> roll(List<Integer> initialRolls) {
        ArrayList<String> result;
        switch (outcome(initialRolls)) {
            case "life":
                result = new ArrayList<>();
                result.add("life");
                break;
            case "stable":
                result = new ArrayList<>();
                result.add("stable");
                break;
            case "death":
                result = new ArrayList<>();
                result.add("death");
                break;
            case "more":
                result = new ArrayList<>();
                for (int i = 20; i > 0; i--) {
                    ArrayList<Integer> rolls = new ArrayList<>();
                    rolls.addAll(initialRolls);
                    rolls.add(i);
                    result.addAll(roll(rolls));
                }
                break;
            default:
                result = new ArrayList<>();
                result.add("error");
                break;
        }
        return result;
    }

    private static String outcome(List<Integer> rolls) {
        if (rolls.contains(20)) {
            return "life";
        } else {
            int countSuc = 0, countFail = 0;
            for (Integer roll : rolls) {
                if (roll >= 10)
                    countSuc++;
                else if (roll == 1)
                    countFail += 2;
                else
                    countFail++;
            }
            if (countSuc >= 3) {
                return "stable";
            } else if (countFail >= 3) {
                return "death";
            } else {
                return "more";
            }
        }
    }

    private static Integer count(List<String> list, String value) {
        Integer result = 0;
        for (String str : list) {
            if (str.equals(value))
                result++;
        }
        return result;
    }

}