The Quick And Dirty RPG

RPG.java

import java.util.Arrays;
import java.util.Collections;
import java.util.List;
import java.util.Random;

/**
 * Created with IntelliJ IDEA.
 * User: Bazlur Rahman Rokon
 * Date: 1/10/13
 * Time: 11:28 PM
 */
public class RPG {
    public static String generate(String allowedCharacters,
                                  boolean mustHaveUppercase, boolean mustHaveDigit,
                                  int minLength, int maxLength) {


        if (minLength > maxLength || minLength < 0 || maxLength < 2) return null;
        if (allowedCharacters.isEmpty()) return null;


        String exclusion = "I1/\\\\";

        String characters = exclude(allowedCharacters, exclusion);
        String chars = removeDuplicateUpercaseLowerCaseSameCharacter(characters);

        String rp = "";

        Random random = new Random();
        int length = random.nextInt(maxLength) + minLength;
        String upperCaseLetter = findUpperCaseLetters(allowedCharacters);
        String digits = findDigits(allowedCharacters);

        if (!mustHaveDigit && !mustHaveUppercase)
            for (int i = 0; i < length; i++) {
                rp += characters.charAt(random.nextInt(chars.length()));
            }

        else if (mustHaveDigit & !mustHaveUppercase) {
            int a = random.nextInt(chars.length() - (length * 2 / 3));
            if (a == 0) ++a;
            for (int i = 0; i < a; i++) {
                rp += digits.charAt(random.nextInt(digits.length()));
            }
            String rest = exclude(chars, digits);
            int b = chars.length() - a;
            for (int i = 0; i < b; i++) {
                rp += rest.charAt(random.nextInt(rest.length()));
            }
        } else if (!mustHaveDigit & mustHaveUppercase) {
            int a = random.nextInt(chars.length() - (length * 2 / 3));
            if (a == 0) ++a;
            for (int i = 0; i < a; i++) {
                rp += upperCaseLetter.charAt(random.nextInt(upperCaseLetter.length()));
            }
            String rest = exclude(chars, upperCaseLetter);
            int b = chars.length() - a;
            for (int i = 0; i < b; i++) {
                rp += rest.charAt(random.nextInt(rest.length()));
            }
        } else if (mustHaveDigit & mustHaveUppercase) {
            int a = random.nextInt(length - (length * 2 / 3));
            if (a == 0) ++a;

            for (int i = 0; i < a; i++) {
                rp += digits.charAt(random.nextInt(digits.length()));
            }
            int b = random.nextInt(length - 2 * a);
            if (b == 0) ++b;
            for (int i = 0; i < b; i++) {
                rp += upperCaseLetter.charAt(random.nextInt(upperCaseLetter.length()));
            }
            String rest = exclude(chars, upperCaseLetter);
            rest = exclude(rest, digits);
            int c = length - (a + b);

            for (int i = 0; i < c; i++) {
                rp += rest.charAt(random.nextInt(rest.length()));
            }
        }
        String pass = removeDuplicateUpercaseLowerCaseSameCharacter(rp);
        return shuffle(pass);
    }

    public static String exclude(String allowedCharacters, String exclusion) {
        return allowedCharacters.replaceAll("[" + exclusion + "]", "");
    }

    private static String findUpperCaseLetters(String allowedCharacters) {
        String letters = "";
        for (int i = 0; i < allowedCharacters.length(); i++) {
            if (Character.isUpperCase(allowedCharacters.charAt(i))) {
                letters += allowedCharacters.charAt(i);
            }
        }
        return letters;
    }

    private static String findDigits(String allowedCharacters) {
        String letters = "";
        for (int i = 0; i < allowedCharacters.length(); i++) {
            if (Character.isDigit(allowedCharacters.charAt(i))) {
                letters += allowedCharacters.charAt(i);
            }
        }
        return letters;
    }

    public static void main(String[] args) {
        String allowedCharacters = "weakPasSWorD1234$*";
        boolean mustHaveUppercase = false;
        boolean mustHaveDigit = false;
        int minLength = 3;
        int maxLength = 20;

            String randomPassword = generate(allowedCharacters,
                    mustHaveUppercase, mustHaveDigit, minLength,
                    maxLength);
            System.out.println("Random password: " + randomPassword);
        
    }

    public static String removeDuplicateUpercaseLowerCaseSameCharacter(String s) {
        if (s.length() <= 1) return s;
        if (s.substring(0, s.length() - 1).toLowerCase().equals(s.substring(s.length() - 1, s.length()).toLowerCase()))
            return removeDuplicateUpercaseLowerCaseSameCharacter(s.substring(0, s.length() - 1));
        else
            return removeDuplicateUpercaseLowerCaseSameCharacter(s.substring(0, s.length() - 1)) + s.substring(s.length() - 1, s.length());
    }

    public static String shuffle(String string) {
        List<String> letters = Arrays.asList(string.split(""));
        Collections.shuffle(letters);
        String shuffled = "";
        for (String letter : letters) {
            shuffled += letter;
        }

        return shuffled;
    }

}