Task: Password generator
C#: using System;
using System.Linq;

class Program
{
    const string Lower = "abcdefghijklmnopqrstuvwxyz";
    const string Upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    const string Digits = "0123456789";
    const string Symbols = "!\"#$%&'()*+,-./:;<=>?@[]^_{|}~";
    static readonly string[] Full = {Lower, Upper, Digits, Symbols, Lower + Upper + Digits + Symbols};

    const string Similar = "Il1O05S2Z";
    static readonly string[] Excluded = Full.Select(x => new string(x.Except(Similar).ToArray())).ToArray();

    static Random _rng = new Random();
    static string[] _symbolSet = Full;

    static void Main(string[] args)
    {
        int length = 12, count = 1;
        try
        {
            foreach (var x in args.Select(arg => arg.Split(':')))
            {
                switch (x[0])
                {
                    case "-l": length = int.Parse(x[1]); break;
                    case "-c": count = int.Parse(x[1]); break;
                    case "-s": _rng = new Random(x[1].GetHashCode()); break;
                    case "-x": _symbolSet = bool.Parse(x[1]) ? Excluded : Full; break;
                    default: throw new FormatException("Could not parse arguments");
                }
            }
        }
        catch { ShowUsage(); return; }
        try
        {
            for (int i = 0; i < count; i++)
                Console.WriteLine(GeneratePass(length));
        }
        catch (Exception ex) { Console.WriteLine("Error: " + ex.Message); }
    }

    static void ShowUsage()
    {
        Console.WriteLine("Usage: PASSGEN [-l:length] [-c:count] [-s:seed] [-x:(true|false)]");
        Console.WriteLine("\t-l: the length of the generated passwords");
        Console.WriteLine("\t-c: the number of passwords to generate");
        Console.WriteLine("\t-s: seed for the random number generator");
        Console.WriteLine("\t-x: exclude similar characters: " + Similar);
        Console.WriteLine("Example: PASSGEN -l:10 -c:5 -s:\"Sample Seed\" -x:true");
    }

    static string GeneratePass(int length)
    {
        var minLength = _symbolSet.Length - 1;
        if(length < minLength)
            throw new Exception("password length must be " + minLength + " or greater");

        int[] usesRemaining = Enumerable.Repeat(1, _symbolSet.Length).ToArray();
        usesRemaining[minLength] = length - minLength;
        var password = new char[length];
        for (int ii = 0; ii < length; ii++)
        {
            int set = _rng.Next(0, _symbolSet.Length);
            if (usesRemaining[set] > 0)
            {
                usesRemaining[set]--;
                password[ii] = _symbolSet[set][_rng.Next(0, _symbolSet[set].Length)];
            }
            else ii--;
        }
        return new string(password);
    }
}

Java: import java.util.*;

public class PasswordGenerator {
    final static Random rand = new Random();

    public static void main(String[] args) {
        int num, len;

        try {
            if (args.length != 2)
                throw new IllegalArgumentException();

            len = Integer.parseInt(args[0]);
            if (len < 4 || len > 16)
                throw new IllegalArgumentException();

            num = Integer.parseInt(args[1]);
            if (num < 1 || num > 10)
                throw new IllegalArgumentException();

            for (String pw : generatePasswords(num, len))
                System.out.println(pw);

        } catch (IllegalArgumentException e) {
            String s = "Provide the length of the passwords (min 4, max 16) you "
                    + "want to generate,\nand how many (min 1, max 10)";
            System.out.println(s);
        }
    }

    private static List<String> generatePasswords(int num, int len) {
        final String s = "!\"#$%&'()*+,-./:;<=>?@[]^_{|}~";

        List<String> result = new ArrayList<>();

        for (int i = 0; i < num; i++) {
            StringBuilder sb = new StringBuilder();
            sb.append(s.charAt(rand.nextInt(s.length())));
            sb.append((char) (rand.nextInt(10) + '0'));
            sb.append((char) (rand.nextInt(26) + 'a'));
            sb.append((char) (rand.nextInt(26) + 'A'));

            for (int j = 4; j < len; j++) {
                int r = rand.nextInt(93) + '!';
                if (r == 92 || r == 96) {
                    j--;
                } else {
                    sb.append((char) r);
                }
            }
            result.add(shuffle(sb));
        }
        return result;
    }

    public static String shuffle(StringBuilder sb) {
        int len = sb.length();
        for (int i = len - 1; i > 0; i--) {
            int r = rand.nextInt(i);
            char tmp = sb.charAt(i);
            sb.setCharAt(i, sb.charAt(r));
            sb.setCharAt(r, tmp);
        }
        return sb.toString();
    }
}