BAEL-5562 Check if character is vowel (#12221)

core-java-modules/core-java-string-operations-4/pom.xml

@@ -30,6 +30,12 @@
             <artifactId>commons-lang3</artifactId>
             <version>${apache-commons-lang3.version}</version>
         </dependency>
+        <dependency>
+            <groupId>org.assertj</groupId>
+            <artifactId>assertj-core</artifactId>
+            <version>${assertj.version}</version>
+            <scope>test</scope>
+        </dependency>
     </dependencies>
 
     <build>

core-java-modules/core-java-string-operations-4/src/main/java/com/baeldung/checkvowels/CheckVowels.java

@@ -0,0 +1,38 @@
+package com.baeldung.checkvowels;
+
+import java.util.regex.Pattern;
+
+public class CheckVowels {
+    private static final String VOWELS = "aeiouAEIOU";
+    private static final Pattern VOWELS_PATTERN = Pattern.compile("[aeiou]", Pattern.CASE_INSENSITIVE);
+
+    public static boolean isInVowelsString(char c) {
+        return VOWELS.indexOf(c) != -1;
+    }
+
+    public static boolean isInVowelsString(String c) {
+        return VOWELS.contains(c);
+    }
+
+    public static boolean isVowelBySwitch(char c) {
+        switch (c) {
+        case 'a':
+        case 'e':
+        case 'i':
+        case 'o':
+        case 'u':
+        case 'A':
+        case 'E':
+        case 'I':
+        case 'O':
+        case 'U':
+            return true;
+        default:
+            return false;
+        }
+    }
+
+    public static boolean isVowelByRegex(String c) {
+        return VOWELS_PATTERN.matcher(c).matches();
+    }
+}

core-java-modules/core-java-string-operations-4/src/test/java/com/baeldung/checkvowels/CheckVowelsUnitTest.java

@@ -0,0 +1,51 @@
+package com.baeldung.checkvowels;
+
+import org.junit.jupiter.api.Test;
+
+import static com.baeldung.checkvowels.CheckVowels.*;
+import static org.assertj.core.api.Assertions.*;
+
+class CheckVowelsUnitTest {
+
+    @Test
+    void givenAVowelCharacter_thenInVowelString() {
+        assertThat(isInVowelsString('e')).isTrue();
+    }
+
+    @Test
+    void givenAConsonantCharacter_thenNotInVowelString() {
+        assertThat(isInVowelsString('z')).isFalse();
+    }
+
+    @Test
+    void givenAVowelString_thenInVowelString() {
+        assertThat(isInVowelsString("e")).isTrue();
+    }
+
+    @Test
+    void givenAConsonantString_thenNotInVowelString() {
+        assertThat(isInVowelsString("z")).isFalse();
+    }
+
+    @Test
+    void givenAVowelCharacter_thenInVowelSwitch() {
+        assertThat(isVowelBySwitch('e')).isTrue();
+    }
+
+    @Test
+    void givenAConsonantCharacter_thenNotInVowelSwitch() {
+        assertThat(isVowelBySwitch('z')).isFalse();
+    }
+
+    @Test
+    void givenAVowelString_thenInVowelPattern() {
+        assertThat(isVowelByRegex("e")).isTrue();
+        assertThat(isVowelByRegex("E")).isTrue();
+    }
+
+    @Test
+    void givenAVowelCharacter_thenInVowelPattern() {
+        assertThat(isVowelByRegex(Character.toString('e'))).isTrue();
+        assertThat(isVowelByRegex("E")).isTrue();
+    }
+}