[indexes-of-matches] Get the Indexes of Regex Pattern Matches in Java (#14648)

core-java-modules/core-java-regex-2/src/test/java/com/baeldung/regex/indexesofmatches/IndexesOfMatchesUnitTest.java

@@ -0,0 +1,75 @@
+package com.baeldung.regex.indexesofmatches;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.ArrayList;
+import java.util.LinkedHashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+import org.junit.jupiter.api.Test;
+
+public class IndexesOfMatchesUnitTest {
+    private static final String INPUT = "This line contains <the first value>, <the second value>, and <the third value>.";
+
+    @Test
+    void whenUsingNorCharClass_thenGetExpectedTexts() {
+        Pattern pattern = Pattern.compile("<[^>]*>");
+        Matcher matcher = pattern.matcher(INPUT);
+        List<String> result = new ArrayList<>();
+        while (matcher.find()) {
+            result.add(matcher.group());
+        }
+        assertThat(result).containsExactly("<the first value>", "<the second value>", "<the third value>");
+    }
+
+    @Test
+    void whenCallingMatcherEnd_thenGetIndexesAfterTheMatchSequence() {
+        Pattern pattern = Pattern.compile("456");
+        Matcher matcher = pattern.matcher("0123456789");
+        String result = null;
+        int startIdx = -1;
+        int endIdx = -1;
+        if (matcher.find()) {
+            result = matcher.group();
+            startIdx = matcher.start();
+            endIdx = matcher.end();
+        }
+        assertThat(result).isEqualTo("456");
+        assertThat(startIdx).isEqualTo(4);
+        assertThat(endIdx).isEqualTo(7);
+    }
+
+    @Test
+    void whenUsingMatcherStartAndEnd_thenGetIndexesOfMatches() {
+        Pattern pattern = Pattern.compile("<[^>]*>");
+        Matcher matcher = pattern.matcher(INPUT);
+        List<String> result = new ArrayList<>();
+        Map<Integer, Integer> indexesOfMatches = new LinkedHashMap<>();
+        while (matcher.find()) {
+            result.add(matcher.group());
+            indexesOfMatches.put(matcher.start(), matcher.end());
+        }
+        assertThat(result).containsExactly("<the first value>", "<the second value>", "<the third value>");
+        assertThat(indexesOfMatches.entrySet()).map(entry -> INPUT.substring(entry.getKey(), entry.getValue()))
+          .containsExactly("<the first value>", "<the second value>", "<the third value>");
+    }
+
+    @Test
+    void whenUsingMatcherStartAndEndWithGroupIdx_thenGetIndexesOfMatches() {
+        Pattern pattern = Pattern.compile("<([^>]*)>");
+        Matcher matcher = pattern.matcher(INPUT);
+        List<String> result = new ArrayList<>();
+        Map<Integer, Integer> indexesOfMatches = new LinkedHashMap<>();
+        while (matcher.find()) {
+            result.add(matcher.group(1));
+            indexesOfMatches.put(matcher.start(1), matcher.end(1));
+        }
+        assertThat(result).containsExactly("the first value", "the second value", "the third value");
+
+        assertThat(indexesOfMatches.entrySet()).map(entry -> INPUT.substring(entry.getKey(), entry.getValue()))
+          .containsExactly("the first value", "the second value", "the third value");
+    }
+}