AsciiAlphaComparator

import java.util.Comparator;

public class AsciiAlphaComparator implements Comparator<String> {

  int compareRight(String a, String b) {
		int bias = 0;
		int ia = 0;
		int ib = 0;

		// The longest run of digits wins.  That aside, the greatest
		// value wins, but we can't know that it will until we've scanned
		// both numbers to know that they have the same magnitude, so we
		// remember it in BIAS.
		for (;; ia++, ib++) {
			char ca = charAt(a, ia);
			char cb = charAt(b, ib);

			if (!Character.isDigit(ca) && !Character.isDigit(cb)) {
				return bias;
			} else if (!Character.isDigit(ca)) {
				return -1;
			} else if (!Character.isDigit(cb)) {
				return +1;
			} else if (ca < cb) {
				if (bias == 0) {
					bias = -1;
				}
			} else if (ca > cb) {
				if (bias == 0)
					bias = +1;
			} else if (ca == 0 && cb == 0) {
				return bias;
			}
		}
	}

	public int compare(String a, String b) {

		int ia = 0, ib = 0;
		int nza = 0, nzb = 0;
		char ca, cb;
		int result;

		while (true) {
			// only count the number of zeroes leading the last number compared
			nza = nzb = 0;

			ca = charAt(a, ia);
			cb = charAt(b, ib);

			// skip over leading spaces or zeros
			while (Character.isSpaceChar(ca) || ca == '0') {
				if (ca == '0') {
					nza++;
				} else {
					// only count consecutive zeroes
					nza = 0;
				}

				ca = charAt(a, ++ia);
			}

			while (Character.isSpaceChar(cb) || cb == '0') {
				if (cb == '0') {
					nzb++;
				} else {
					// only count consecutive zeroes
					nzb = 0;
				}

				cb = charAt(b, ++ib);
			}

			// process run of digits
			if (Character.isDigit(ca) && Character.isDigit(cb)) {
				if ((result = compareRight(a.substring(ia), b
						.substring(ib))) != 0) {
					return result;
				}
			}

			if (ca == 0 && cb == 0) {
				// The strings compare the same.  Perhaps the caller
				// will want to call strcmp to break the tie.
				return nza - nzb;
			}

			if (ca < cb) {
				return -1;
			} else if (ca > cb) {
				return +1;
			}

			++ia;
			++ib;
		}
	}

	static char charAt(String s, int i) {
		if (s == null || i >= s.length()) {
			return 0;
		}
		return s.charAt(i);
	}	

}