Adding files for BAEL-2543

core-java/src/main/java/com/baeldung/keyword/Circle.java

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+package com.baeldung.keyword;
+
+public class Circle extends Round implements Shape {
+}

core-java/src/main/java/com/baeldung/keyword/Ring.java

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+package com.baeldung.keyword;
+
+public class Ring extends Round {
+}

core-java/src/main/java/com/baeldung/keyword/Round.java

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+package com.baeldung.keyword;
+
+public class Round {
+}

core-java/src/main/java/com/baeldung/keyword/Shape.java

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+package com.baeldung.keyword;
+
+public interface Shape {
+}

core-java/src/main/java/com/baeldung/keyword/Triangle.java

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+package com.baeldung.keyword;
+
+public class Triangle implements Shape {
+}

core-java/src/test/java/com/baeldung/keyword/test/InstanceOfUnitTest.java

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+package com.baeldung.keyword.test;
+
+import org.junit.Assert;
+import org.junit.jupiter.api.Test;
+
+import com.baeldung.keyword.Circle;
+import com.baeldung.keyword.Ring;
+import com.baeldung.keyword.Round;
+import com.baeldung.keyword.Shape;
+import com.baeldung.keyword.Triangle;
+
+public class InstanceOfUnitTest {
+
+    @Test
+    public void giveWhenInstanceIsCorrect_thenReturnTrue() {
+        Ring ring = new Ring();
+        Assert.assertTrue("ring is instance of Round ", ring instanceof Round);
+    }
+
+    @Test
+    public void giveWhenObjectIsInstanceOfType_thenReturnTrue() {
+        Circle circle = new Circle();
+        Assert.assertTrue("circle is instance of Circle ", circle instanceof Circle);
+    }
+
+  
+    @Test
+    public void giveWhenInstanceIsOfSubtype_thenReturnTrue() {
+        Circle circle = new Circle();
+        Assert.assertTrue("circle is instance of Round", circle instanceof Round);
+    }
+
+    @Test
+    public void giveWhenTypeIsInterface_thenReturnTrue() {
+        Circle circle = new Circle();
+        Assert.assertTrue("circle is instance of Shape", circle instanceof Shape);
+    }
+
+    @Test
+    public void giveWhenInstanceValueIsNull_thenReturnFalse() {
+        Circle circle = null;
+        Assert.assertFalse("circle is instance of Round", circle instanceof Round);
+    }
+
+    @Test
+    public void giveWhenComparingClassInDiffHierarchy_thenCompilationError() {
+        // Assert.assertFalse("circle is instance of Triangle", circle instanceof Triangle);
+    }
+}