BAEL-5025 Example code for camel case to words (#10964)

core-java-modules/core-java-regex-2/src/main/java/com/baeldung/regex/camelcasetowords/CamelCaseToWords.java

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+package com.baeldung.regex.camelcasetowords;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * Convert a string in camelCase or TitleCase into a list of words
+ */
+public class CamelCaseToWords {
+    private static final Pattern WORD_FINDER = Pattern.compile("(([A-Z]?[a-z]+)|([A-Z]))");
+
+    /**
+     * Find the words in mixed case string like ThisIsText or HereIsSomeText
+     * @param text the text to parse
+     * @return the list of words to process
+     */
+    public static List<String> findWordsInMixedCase(String text) {
+        Matcher matcher = WORD_FINDER.matcher(text);
+        List<String> words = new ArrayList<>();
+        while (matcher.find()) {
+            words.add(matcher.group(0));
+        }
+        return words;
+    }
+}

core-java-modules/core-java-regex-2/src/main/java/com/baeldung/regex/camelcasetowords/Recapitalize.java

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+package com.baeldung.regex.camelcasetowords;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class Recapitalize {
+    private static final Set<String> STOP_WORDS = Stream.of("a", "an", "the", "and",
+      "but", "for", "at", "by", "to", "or")
+      .collect(Collectors.toSet());
+
+    public static String sentenceCase(List<String> words) {
+        List<String> capitalized = new ArrayList<>();
+        for (int i = 0; i < words.size(); i++) {
+            String currentWord = words.get(i);
+            if (i == 0) {
+                capitalized.add(capitalizeFirst(currentWord));
+            } else {
+                capitalized.add(currentWord.toLowerCase());
+            }
+        }
+        return String.join(" ", capitalized) + ".";
+    }
+
+    public static String capitalizeMyTitle(List<String> words) {
+        List<String> capitalized = new ArrayList<>();
+        for (int i = 0; i < words.size(); i++) {
+            String currentWord = words.get(i);
+            if (i == 0 || !STOP_WORDS.contains(currentWord.toLowerCase())) {
+                capitalized.add(capitalizeFirst(currentWord));
+            } else {
+                capitalized.add(currentWord.toLowerCase());
+            }
+        }
+        return String.join(" ", capitalized);
+    }
+
+    private static String capitalizeFirst(String word) {
+        return word.substring(0, 1).toUpperCase() + word.substring(1).toLowerCase();
+    }
+}

core-java-modules/core-java-regex-2/src/test/java/com/baeldung/regex/camelcasetowords/CamelCaseToWordsUnitTest.java

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+package com.baeldung.regex.camelcasetowords;
+
+import org.junit.jupiter.api.Test;
+
+import static com.baeldung.regex.camelcasetowords.CamelCaseToWords.findWordsInMixedCase;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class CamelCaseToWordsUnitTest {
+
+    @Test
+    void givenPlainStringWithNonLetters_thenFindsWords() {
+        assertThat(findWordsInMixedCase("some words"))
+          .containsExactly("some", "words");
+    }
+
+    @Test
+    void givenWordsInCamelCase_thenFindsWords() {
+        assertThat(findWordsInMixedCase("thisIsCamelCaseText"))
+          .containsExactly("this", "Is", "Camel", "Case", "Text");
+    }
+
+    @Test
+    void givenWordsInTitleCase_thenFindsWords() {
+        assertThat(findWordsInMixedCase("ThisIsTitleCaseText"))
+          .containsExactly("This", "Is", "Title", "Case", "Text");
+    }
+
+    @Test
+    void givenWordsAcrossMultipleTexts_thenFindsWords() {
+        assertThat(findWordsInMixedCase("ThisIsTitleCaseText --- andSoIsThis"))
+          .containsExactly("This", "Is", "Title", "Case", "Text", "and", "So", "Is", "This");
+    }
+
+    @Test
+    void givenCamelCaseHasASingleLetterWord_thenItCanBeSplit() {
+        assertThat(findWordsInMixedCase("thisHasASingleLetterWord"))
+          .containsExactly("this", "Has", "A", "Single", "Letter", "Word");
+    }
+}

core-java-modules/core-java-regex-2/src/test/java/com/baeldung/regex/camelcasetowords/RecapitalizeUnitTest.java

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+package com.baeldung.regex.camelcasetowords;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+import static com.baeldung.regex.camelcasetowords.Recapitalize.*;
+import static org.assertj.core.api.Assertions.assertThat;
+
+class RecapitalizeUnitTest {
+
+    @Test
+    void givenWords_thenCanComposeSentence() {
+        assertThat(sentenceCase(Arrays.asList("these", "Words", "Form", "A", "Sentence")))
+          .isEqualTo("These words form a sentence.");
+    }
+
+    @Test
+    void givenNonStopWords_thenTitleIsComposed() {
+        assertThat(capitalizeMyTitle(Arrays.asList("title", "words", "capitalize")))
+          .isEqualTo("Title Words Capitalize");
+    }
+
+    @Test
+    void givenStopWords_thenTitleHasThemInLowerCase() {
+        assertThat(capitalizeMyTitle(Arrays.asList("this", "is", "A", "title", "with", "a", "stop", "word", "or", "two")))
+          .isEqualTo("This Is a Title With a Stop Word or Two");
+    }
+
+    @Test
+    void givenStopWordIsFirstWord_thenTitleHasItCapitalized() {
+        assertThat(capitalizeMyTitle(Arrays.asList("a", "stop", "word", "first")))
+          .isEqualTo("A Stop Word First");
+    }
+}