Compare characters by value in DamerauLevenshteinDistance

src/main/java/org/apache/commons/text/similarity/DamerauLevenshteinDistance.java

@@ -16,6 +16,8 @@
  */
 package org.apache.commons.text.similarity;
 
+import java.util.Objects;
+
 /**
  * An algorithm for measuring the difference between two character sequences using the
  * <a href="https://en.wikipedia.org/wiki/Damerau%E2%80%93Levenshtein_distance">Damerau-Levenshtein Distance</a>.
@@ -32,7 +34,7 @@ public class DamerauLevenshteinDistance implements EditDistance<Integer> {
 
     private static <E> int calculateCost(final SimilarityInput<E> left, final SimilarityInput<E> right, final int leftIndex, final int rightIndex,
             final int[] curr, final int[] prev, final int[] prevPrev) {
-        final int cost = left.at(leftIndex - 1) == right.at(rightIndex - 1) ? 0 : 1;
+        final int cost = Objects.equals(left.at(leftIndex - 1), right.at(rightIndex - 1)) ? 0 : 1;
         // Select cheapest operation
         int value = Math.min(
                 Math.min(
@@ -44,8 +46,8 @@ private static <E> int calculateCost(final SimilarityInput<E> left, final Simila
         // Check if adjacent characters are the same -> transpose if cheaper
         if (leftIndex > 1
                 && rightIndex > 1
-                && left.at(leftIndex - 1) == right.at(rightIndex - 2)
-                && left.at(leftIndex - 2) == right.at(rightIndex - 1)) {
+                && Objects.equals(left.at(leftIndex - 1), right.at(rightIndex - 2))
+                && Objects.equals(left.at(leftIndex - 2), right.at(rightIndex - 1))) {
             // Use cost here, to properly handle two subsequent equal letters
             value = Math.min(value, prevPrev[rightIndex - 2] + cost);
         }

src/test/java/org/apache/commons/text/similarity/DamerauLevenshteinDistanceTest.java

@@ -77,7 +77,14 @@ static Stream<Arguments> limitedDamerauLevenshteinDistanceTestCases() {
                 Arguments.of("xyxyxyxyxy", "yxyxyxyxyx", 4, 2),
                 Arguments.of("aaaaabbbbbccccc", "cccccbbbbbaaaaa", 5, -1),
                 Arguments.of("thequickbrownfoxjumpsoverthelazydog", "thequickbrownfoxjumpsovrethelazydog", 1, 1),
-                Arguments.of("antidisestablishmentarianism", "antidisestablishmentarianisn", 3, 1)
+                Arguments.of("antidisestablishmentarianism", "antidisestablishmentarianisn", 3, 1),
+                // Non-ASCII characters are outside the Character.valueOf cache, so identical inputs must still measure zero.
+                Arguments.of("caf\u00e9", "caf\u00e9", 1, 0),
+                Arguments.of("\u4f60\u597d", "\u4f60\u597d", 1, 0),
+                Arguments.of("na\u00efve", "na\u00efve", 1, 0),
+                // Transposing two adjacent non-ASCII characters costs one edit, exactly as it does for ASCII.
+                Arguments.of("caf\u00e9\u00e8", "caf\u00e8\u00e9", 1, 1),
+                Arguments.of("\u4f60\u597d", "\u597d\u4f60", 1, 1)
         );
     }
 
@@ -123,7 +130,16 @@ static Stream<Arguments> unlimitedDamerauLevenshteinDistanceTestCases() {
                 Arguments.of("xyxyxyxyxy", "yxyxyxyxyx", 2),
                 Arguments.of("aaaaabbbbbccccc", "cccccbbbbbaaaaa", 10),
                 Arguments.of("thequickbrownfoxjumpsoverthelazydog", "thequickbrownfoxjumpsovrethelazydog", 1),
-                Arguments.of("antidisestablishmentarianism", "antidisestablishmentarianisn", 1)
+                Arguments.of("antidisestablishmentarianism", "antidisestablishmentarianisn", 1),
+                // Non-ASCII characters are outside the Character.valueOf cache, so identical inputs must still measure zero.
+                Arguments.of("caf\u00e9", "caf\u00e9", 0),
+                Arguments.of("\u4f60\u597d", "\u4f60\u597d", 0),
+                Arguments.of("na\u00efve", "na\u00efve", 0),
+                Arguments.of("\ud83d\ude00", "\ud83d\ude00", 0),
+                // Transposing two adjacent non-ASCII characters costs one edit, exactly as it does for ASCII.
+                Arguments.of("caf\u00e9\u00e8", "caf\u00e8\u00e9", 1),
+                Arguments.of("\u4f60\u597d", "\u597d\u4f60", 1),
+                Arguments.of("\u00e9x", "x\u00e9", 1)
         );
     }