RandomPasswordGenerator

import java.util.Random;

public class RandomPasswordGenerator {
    private static final String CAPITAL_LETTERS =
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    private static final String SMALL_LETTERS =
        "abcdefghijklmnopqrstuvwxyz";
    private static final String DIGITS = "0123456789";
    //private static final String SPECIAL_CHARS =
    //    "~!@#$%^&*()_+=`{}[]\\|':;.,/?<>";
    private static final String SPECIAL_CHARS =
        "!@#$%&.";

    private static final String ALL_CHARS =
        CAPITAL_LETTERS + SMALL_LETTERS + DIGITS + SPECIAL_CHARS;
    private static Random rnd = new Random();
    public static void main(String[] args) {
        StringBuilder password = new StringBuilder();

        // Generate two random capital letters
        for (int i=1; i<=4; i++) {
            char capitalLetter = generateChar(CAPITAL_LETTERS);
            insertAtRandomPosition(password, capitalLetter);
        }

        // Generate two random small letters
        for (int i=1; i<=4; i++) {
            char smallLetter = generateChar(SMALL_LETTERS);
            insertAtRandomPosition(password, smallLetter);
        }

        // Generate one random digit
        for (int i=1; i<=3; i++) {
            char digit = generateChar(DIGITS);
            insertAtRandomPosition(password, digit);
            }

        // Generate 3 special characters
        for (int i=1; i<=3; i++) {
            char specialChar = generateChar(SPECIAL_CHARS);
            insertAtRandomPosition(password, specialChar);
        }

        // Generate few random characters (between 0 and 7)
        int count = rnd.nextInt(8);
        for (int i=1; i<=count; i++) {
            char specialChar = generateChar(ALL_CHARS);
            insertAtRandomPosition(password, specialChar);
        }

        System.out.println(password);
    }

    private static void insertAtRandomPosition(
            StringBuilder password, char character) {
        int randomPosition = rnd.nextInt(password.length()+1);
        password.insert(randomPosition, character);
    }

    private static char generateChar(String availableChars) {
        int randomIndex = rnd.nextInt(availableChars.length());
        char randomChar = availableChars.charAt(randomIndex);
        return randomChar;
    }

}