A basic Java version of the Jaro-Winkler distance algorithm for measuring the similarity of Strings. It offers good performance on shorter types of strings like names, etc.

JaroWinklerScore.java

public class JaroWinklerScore {
    /**
	 * Applies the Jaro-Winkler distance algorithm to the given strings, providing information about the
	 * similarity of them.
	 * 
	 * @param s1 The first string that gets compared. May be <code>null</node> or empty.
	 * @param s2 The second string that gets compared. May be <code>null</node> or empty.
	 * @return The Jaro-Winkler score (between 0.0 and 1.0), with a higher value indicating larger similarity.
	 * 
	 * @author Thomas Trojer <[email protected]>
	 */
	public static double compute(final String s1, final String s2) {
		// lowest score on empty strings
		if (s1 == null || s2 == null || s1.isEmpty() || s2.isEmpty()) {
			return 0;
		}
		// highest score on equal strings
		if (s1.equals(s2)) {
			return 1;
		}
		// some score on different strings
		int prefixMatch = 0; // exact prefix matches
		int matches = 0; // matches (including prefix and ones requiring transpostion)
		int transpositions = 0; // matching characters that are not aligned but close together 
		int maxLength = Math.max(s1.length(), s2.length());
		int maxMatchDistance = Math.max((int) Math.floor(maxLength / 2.0) - 1, 0); // look-ahead/-behind to limit transposed matches
		// comparison
		final String shorter = s1.length() < s2.length() ? s1 : s2;
		final String longer = s1.length() >= s2.length() ? s1 : s2;
		for (int i = 0; i < shorter.length(); i++) {
		    // check for exact matches
			boolean match = shorter.charAt(i) == longer.charAt(i);
			if (match) {
				if (i < 4) {
					// prefix match (of at most 4 characters, as described by the algorithm)
					prefixMatch++;
				}
				matches++;
				continue;
			}
			// check fro transposed matches
			for (int j = Math.max(i - maxMatchDistance, 0); j < Math.min(i + maxMatchDistance, longer.length()); j++) {
				if (i == j) {
					// case already covered
					continue;
				}
				// transposition required to match?
				match = shorter.charAt(i) == longer.charAt(j);
				if (match) {
					transpositions++;
					break;
				}
			}
		}
		// any matching characters?
		if (matches == 0) {
			return 0;
		}
		// modify transpositions (according to the algorithm)
		transpositions = (int) (transpositions / 2.0);
		// non prefix-boosted score
		double score = 0.3334 * (matches / (double) longer.length() + matches / (double) shorter.length() + (matches - transpositions)
				/ (double) matches);
		if (score < 0.7) {
			return score;
		}
		// we already have a good match, hence we boost the score proportional to the common prefix
		double boostedScore = score + prefixMatch * 0.1 * (1.0 - score);
		return boostedScore;
	}
}

Why "if (score < 0.7)" is needed?

Why "if (score < 0.7)" is needed?

That is Winkler's rule. Winkler basically added a "boost" or modification to the score of a matching string if its score was over a certain threshold. If the score is under that threshold then the score would be returned unmodified.