http://www.satisfice.com/blog/archives/22

CounterString.java

import java.io.IOException;

/**
 * A class for generateing <i>counterstring</i>s.
 *
 * @author Jin Kwon &lt;onacit_at_gmail.com&gt;
 * @see <a href="http://www.satisfice.com/blog/archives/22">Counterstrings: Self-Describing Test Data</a>
 */
public class CounterString {

    /**
     * Generates a <i>counterstring</i> of specified length by appending characters to given appendable.
     *
     * @param appendable the appendable into which generated characters are appended.
     * @param length     the length of the <i>counterstring</i>.
     * @param radix      a radix for numeric characters.
     * @param <T>        appendable type parameter.
     * @return given appendable.
     * @throws IOException if an I/O error occurs.
     * @see Integer#toString(int, int)
     */
    public static <T extends Appendable> T generate(final T appendable, final int length, final int radix)
            throws IOException {
        if (appendable == null) {
            throw new NullPointerException("appendable is null");
        }
        if (length < 0) {
            throw new IllegalArgumentException("length(" + length + ") < 0");
        }
        int l = 0;
        for (int c = 0; l < length; c++) {
            final String s = Integer.toString(c, radix);
            if (l + s.length() == c - 1) {
                if (l + s.length() + 1 > length) {
                    appendable.append(s, 0, length - l);
                    break;
                }
                appendable.append(s);
                l += s.length();
                appendable.append('*');
                l++;
            }
        }
        return appendable;
    }

    /**
     * The main class of this program whose first argument is the {@code length} and the second optional argument is a
     * {@code radix}.
     *
     * @param args command line argument.
     * @throws IOException if an I/O error occurs.
     */
    public static void main(final String... args) throws IOException {
        final int length = Integer.parseInt(args[0]);
        int radix = 10;
        try {
            radix = Integer.parseInt(args[1]);
        } catch (final ArrayIndexOutOfBoundsException aioobe) {
        }
        final StringBuilder appendable = generate(new StringBuilder(length), length, radix);
        assert appendable.length() == length;
        System.out.println(appendable.toString());
    }
}