[if-class-is-enum] check class is enum (#15235)

* [if-class-is-enum] check class is enum

* [if-class-is-enum] move to new module

core-java-modules/core-java-lang-oop-types-2/src/test/java/com/baeldung/enums/classcheck/CheckClassIsEnumUnitTest.java

@@ -0,0 +1,75 @@
+package com.baeldung.enums.classcheck;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+enum Device {
+    Keyboard, Monitor, Mouse, Printer
+}
+
+enum Weekday {
+    Monday, Tuesday, Wednesday, Thursday, Friday,
+    Saturday {
+        @Override
+        boolean isWeekend() {
+            return true;
+        }
+    },
+    Sunday {
+        @Override
+        boolean isWeekend() {
+            return true;
+        }
+    };
+
+    boolean isWeekend() {
+        return false;
+    }
+}
+
+public class CheckClassIsEnumUnitTest {
+
+    @Test
+    void whenUsingInstanceOf_thenGetExpectedResult() {
+        Object obj = Device.Keyboard;
+        assertTrue(obj instanceof Enum);
+    }
+
+    @Test
+    void whenUsingisInstance_thenGetExpectedResult() {
+        Object obj = Device.Keyboard;
+        assertTrue(Enum.class.isInstance(obj));
+    }
+
+    @Test
+    void whenUsingEnumClassisAssignableFrom_thenGetExpectedResult() {
+        Object obj = Device.Keyboard;
+        assertTrue(Enum.class.isAssignableFrom(obj.getClass()));
+    }
+
+    @Test
+    void whenUsingGetClassIsEnum_thenGetExpectedResult() {
+        assertTrue(Device.class.isEnum());
+
+        Object obj = Device.Keyboard;
+        assertTrue(obj.getClass().isEnum());
+    }
+
+
+    @Test
+    void whenEnum_thenGetExpectedResult() {
+        Object monday = Weekday.Monday;
+        assertTrue(monday instanceof Enum);
+        assertTrue(Enum.class.isInstance(monday));
+        assertTrue(Enum.class.isAssignableFrom(monday.getClass()));
+        assertTrue(monday.getClass().isEnum());
+
+        Object sunday = Weekday.Sunday;
+        assertTrue(sunday instanceof Enum);
+        assertTrue(Enum.class.isInstance(sunday));
+        assertTrue(Enum.class.isAssignableFrom(sunday.getClass()));
+        assertFalse(sunday.getClass().isEnum()); // <-- isEnum() check failed when Enum values with body
+    }
+}