JavaAlgorithms/Others/PasswordGen.java

package Others;

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

/**
 * Creates a random password from ASCII letters Given password length bounds
 *
 * @author AKS1996
 * @date 2017.10.25
 */
class PasswordGen {
  public static void main(String args[]) {
    String password = generatePassword(8, 16);
    System.out.print("Password: " + password);
  }

  static String generatePassword(int min_length, int max_length) {
    Random random = new Random();

    String upper = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    String lower = "abcdefghijklmnopqrstuvwxyz";
    String numbers = "0123456789";
    String specialChars = "!@#$%^&*(){}?";

    String allChars = upper + lower + numbers + specialChars;

    List<Character> letters = new ArrayList<Character>();
    for (char c : allChars.toCharArray()) letters.add(c);

    // Inbuilt method to randomly shuffle a elements of a list
    Collections.shuffle(letters);
    StringBuilder password = new StringBuilder();

    // Note that size of the password is also random
    for (int i = random.nextInt(max_length - min_length) + min_length; i > 0; --i) {
      password.append(letters.get(random.nextInt(letters.size())));
    }

    return password.toString();
  }
}