[BAEL-4532]a.getClass() vs A.class

sk1418 · sk1418 · commit 81f2109ae4b4 · 2020-09-26T19:25:36.000+02:00
diff --git a/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/Animal.java b/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/Animal.java
@@ -0,0 +1,5 @@
+package com.baeldung.getclassobject;
+
+public class Animal {
+    protected int numberOfEyes;
+}
diff --git a/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/Monkey.java b/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/Monkey.java
@@ -0,0 +1,4 @@
+package com.baeldung.getclassobject;
+
+public class Monkey extends Animal {
+}
diff --git a/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/SomeAbstractClass.java b/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/SomeAbstractClass.java
@@ -0,0 +1,4 @@
+package com.baeldung.getclassobject;
+
+public abstract class SomeAbstractClass {
+}
diff --git a/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/SomeInterface.java b/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/SomeInterface.java
@@ -0,0 +1,4 @@
+package com.baeldung.getclassobject;
+
+interface SomeInterface {
+}
diff --git a/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/SomeUtils.java b/core-java-modules/core-java-lang-3/src/main/java/com/baeldung/getclassobject/SomeUtils.java
@@ -0,0 +1,9 @@
+package com.baeldung.getclassobject;
+
+public class SomeUtils {
+    private SomeUtils() {
+        throw new RuntimeException("This Util class is not allowed to be instantiated!");
+    }
+    //  public static utilMethods
+    //  ...
+}
diff --git a/core-java-modules/core-java-lang-3/src/test/java/com/baeldung/getclassobject/GetClassObjectUnitTest.java b/core-java-modules/core-java-lang-3/src/test/java/com/baeldung/getclassobject/GetClassObjectUnitTest.java
@@ -0,0 +1,55 @@
+package com.baeldung.getclassobject;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class GetClassObjectUnitTest {
+    @Test
+    public void givenObjectAndType_whenGettingClassObject_thenTwoMethodsHaveTheSameResult() {
+        String str = "I am an object of the String class";
+        Class fromStrObject = str.getClass();
+        Class clazz = String.class;
+        assertSame(fromStrObject, clazz);
+    }
+
+    @Test
+    public void givenClassInheritance_whenGettingRuntimeTypeAndStaticType_thenGetDifferentResult() {
+        Animal animal = new Monkey();
+        Class runtimeType = animal.getClass();
+        Class staticType = Animal.class;
+        //Not equals
+        assertNotEquals(staticType, runtimeType);
+
+        Class monkeyClass = Monkey.class;
+        assertSame(runtimeType, monkeyClass);
+    }
+
+    @Test
+    public void givenPrimitiveType_whenGettingClassObject_thenOnlyStaticTypeWorks() {
+        int number = 7;
+        // Class numberClass = number.getClass();   <-- compilation error
+        Class intType = int.class;
+
+        assertNotNull(intType);
+        assertEquals("int", intType.getName());
+        assertTrue(intType.isPrimitive());
+    }
+
+    @Test
+    public void givenTypeCannotInstantiate_whenGetTypeStatically_thenGetTypesSuccefully() {
+        Class interfaceType = SomeInterface.class;
+        Class abstractClassType = SomeAbstractClass.class;
+        Class utilClassType = SomeUtils.class;
+
+        assertNotNull(interfaceType);
+        assertTrue(interfaceType.isInterface());
+        assertEquals("SomeInterface", interfaceType.getSimpleName());
+
+        assertNotNull(abstractClassType);
+        assertEquals("SomeAbstractClass", abstractClassType.getSimpleName());
+
+        assertNotNull(utilClassType);
+        assertEquals("SomeUtils", utilClassType.getSimpleName());
+    }
+}

-Original file line number
+Diff line change
@@ @@ -0,0 +1,4 @@ @@
 +package com.baeldung.getclassobject;
++
 +public class Monkey extends Animal {
 +}