[str-all-upper] Check if a String is All Uppercase or Lowercase in Java (#14227)

core-java-modules/core-java-string-operations-6/pom.xml

@@ -12,6 +12,14 @@
         <artifactId>core-java-modules</artifactId>
         <version>0.0.1-SNAPSHOT</version>
     </parent>
+    <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-lang3</artifactId>
+            <version>${apache.commons-lang.version}</version>
+        </dependency>
+
+    </dependencies>
 
     <build>
         <plugins>
@@ -29,6 +37,7 @@
     <properties>
         <maven.compiler.source>11</maven.compiler.source>
         <maven.compiler.target>11</maven.compiler.target>
+        <apache.commons-lang.version>3.12.0</apache.commons-lang.version>
     </properties>
 
 </project>

core-java-modules/core-java-string-operations-6/src/test/java/com/baeldung/checkcase/StringAllUpperOrLowercaseUnitTest.java

@@ -0,0 +1,104 @@
+package com.baeldung.checkcase;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.apache.commons.lang3.StringUtils;
+import org.junit.jupiter.api.Test;
+
+class CaseChecker {
+
+    static boolean allUpper1(String input) {
+        return input.equals(input.toUpperCase());
+    }
+
+    static boolean allLower1(String input) {
+        return input.equals(input.toLowerCase());
+    }
+
+    static boolean allUpper2(String input) {
+        for (char c : input.toCharArray()) {
+            //  don't write in this way: if (!Character.isUpperCase(c))
+            if (Character.isLowerCase(c)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    static boolean allLower2(String input) {
+        for (char c : input.toCharArray()) {
+            //  don't write in this way: if (!Character.isLowerCase(c))
+            if (Character.isUpperCase(c)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    static boolean allUpper3(String input) {
+        return input.chars()
+          .noneMatch(Character::isLowerCase);
+    }
+
+    static boolean allLower3(String input) {
+        return input.chars()
+          .noneMatch(Character::isUpperCase);
+    }
+}
+
+public class StringAllUpperOrLowercaseUnitTest {
+    private static final String UPPER_INPUT = "1: COOL!";
+    private static final String LOWER_INPUT = "2: cool!";
+    private static final String MIXED_INPUT = "3: Cool！";
+
+    @Test
+    void whenComparingToConvertedString_thenGetExpectedResult() {
+        assertTrue(CaseChecker.allLower1(LOWER_INPUT));
+        assertFalse(CaseChecker.allLower1(UPPER_INPUT));
+        assertFalse(CaseChecker.allLower1(MIXED_INPUT));
+
+        assertFalse(CaseChecker.allUpper1(LOWER_INPUT));
+        assertTrue(CaseChecker.allUpper1(UPPER_INPUT));
+        assertFalse(CaseChecker.allUpper1(MIXED_INPUT));
+    }
+
+    @Test
+    void whenCheckCharInArray_thenGetExpectedResult() {
+        assertTrue(CaseChecker.allLower2(LOWER_INPUT));
+        assertFalse(CaseChecker.allLower2(UPPER_INPUT));
+        assertFalse(CaseChecker.allLower2(MIXED_INPUT));
+
+        assertFalse(CaseChecker.allUpper2(LOWER_INPUT));
+        assertTrue(CaseChecker.allUpper2(UPPER_INPUT));
+        assertFalse(CaseChecker.allUpper2(MIXED_INPUT));
+    }
+
+    @Test
+    void whenUsingStream_thenGetExpectedResult() {
+        assertTrue(CaseChecker.allLower3(LOWER_INPUT));
+        assertFalse(CaseChecker.allLower3(UPPER_INPUT));
+        assertFalse(CaseChecker.allLower3(MIXED_INPUT));
+
+        assertFalse(CaseChecker.allUpper3(LOWER_INPUT));
+        assertTrue(CaseChecker.allUpper3(UPPER_INPUT));
+        assertFalse(CaseChecker.allUpper3(MIXED_INPUT));
+    }
+
+    @Test
+    void whenUsingApacheCommons_thenGetExpectedResult() {
+        assertFalse(StringUtils.isAllLowerCase(LOWER_INPUT));
+        assertFalse(StringUtils.isAllLowerCase(UPPER_INPUT));
+        assertFalse(StringUtils.isAllLowerCase(MIXED_INPUT));
+
+        assertFalse(StringUtils.isAllLowerCase("a b"));
+        assertTrue(StringUtils.isAllLowerCase("ab"));
+
+        assertFalse(StringUtils.isAllUpperCase(LOWER_INPUT));
+        assertFalse(StringUtils.isAllUpperCase(UPPER_INPUT));
+        assertFalse(StringUtils.isAllUpperCase(MIXED_INPUT));
+
+        assertFalse(StringUtils.isAllUpperCase("A B"));
+        assertTrue(StringUtils.isAllUpperCase("AB"));
+    }
+}