java program random password generator

PasswordGenerator.java

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

/**
 *
 * @author Candid Java
 */
public class PasswordGenerator {

 public static void main(String args[]) {

  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);

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

  String password = "";
  int maxLength = 20; // let consider max length is 20
  int minLength = 9; // let consider min length is 9

  for (int i = random.nextInt(maxLength - minLength) + minLength; i > 0; --i) {
   password += letters.get(random.nextInt(letters.size()));
  }
  System.out.print("Password: " + password); // The size of the password is random
 }

}

Output

Password: n!c4%s$XNgNGrm5