public static String random(int count, int start, int end, final boolean letters, final boolean numbers,
                                final char[] chars, final Random random) {
        if (count == 0) {
            return StringUtils.EMPTY;
        } else if (count < 0) {
            throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
        }
        if (chars != null && chars.length == 0) {
            throw new IllegalArgumentException("The chars array must not be empty");
        }

        if (start == 0 && end == 0) {
            if (chars != null) {
                end = chars.length;
            } else {
                if (!letters && !numbers) {
                    end = Character.MAX_CODE_POINT;
                } else {
                    end = 'z' + 1;
                    start = ' ';
                }
            }
        } else {
            if (end <= start) {
                throw new IllegalArgumentException("Parameter end (" + end + ") must be greater than start (" + start + ")");
            }
        }

        final int zero_digit_ascii = 48;
        final int first_letter_ascii = 65;

        if (chars == null && (numbers && end <= zero_digit_ascii
                || letters && end <= first_letter_ascii)) {
            throw new IllegalArgumentException("Parameter end (" + end + ") must be greater then (" + zero_digit_ascii + ") for generating digits " +
                    "or greater then (" + first_letter_ascii + ") for generating letters.");
        }

        final StringBuilder builder = new StringBuilder(count);
        final int gap = end - start;

        while (count-- != 0) {
            int codePoint;
            if (chars == null) {
                codePoint = random.nextInt(gap) + start;

                switch (Character.getType(codePoint)) {
                    case Character.UNASSIGNED:
                    case Character.PRIVATE_USE:
                    case Character.SURROGATE:
                        count++;
                        continue;
                }

            } else {
                codePoint = chars[random.nextInt(gap) + start];
            }

            final int numberOfChars = Character.charCount(codePoint);
            if (count == 0 && numberOfChars > 1) {
                count++;
                continue;
            }

            if (letters && Character.isLetter(codePoint)
                    || numbers && Character.isDigit(codePoint)
                    || !letters && !numbers) {
                builder.appendCodePoint(codePoint);

                if (numberOfChars == 2) {
                    count--;
                }

            } else {
                count++;
            }
        }
        return builder.toString();
    }
<p>Creates a random string based on a variety of options, using
supplied source of randomness.</p>

<p>If start and end are both {@code 0}, start and end are set
to {@code ' '} and {@code 'z'}, the ASCII printable
characters, will be used, unless letters and numbers are both
{@code false}, in which case, start and end are set to
{@code 0} and {@link Character#MAX_CODE_POINT}.

<p>If set is not {@code null}, characters between start and
end are chosen.</p>

<p>This method accepts a user-supplied {@link Random}
instance to use as a source of randomness. By seeding a single
{@link Random} instance with a fixed seed and using it for each call,
the same random sequence of strings can be generated repeatedly
and predictably.</p>

@param count   the length of random string to create
@param start   the position in set of chars to start at (inclusive)
@param end     the position in set of chars to end before (exclusive)
@param letters only allow letters?
@param numbers only allow numbers?
@param chars   the set of chars to choose randoms from, must not be empty.
               If {@code null}, then it will use the set of all chars.
@param random  a source of randomness.
@return the random string
@throws ArrayIndexOutOfBoundsException if there are not
                                       {@code (end - start) + 1} characters in the set array.
@throws IllegalArgumentException       if {@code count} &lt; 0 or the provided chars array is empty.
@since 2.0
android/android_framework/base/src/main/java/lang3/RandomStringUtils.java