BAEL-2431 Implementing multi-inheritance and Polymorphism using interfaces (#5924)

* Implementing Hexagonal Architecture in java

* Implementing multi-inheritance and Polymorphism using interfaces

* Removing hexagonal code

* Deleting hexagonal architecture code

* fix for unit test names

core-java-8/src/test/java/com/baeldung/interfaces/PolymorphysimUnitTest.java

@@ -0,0 +1,26 @@
+package com.baeldung.interfaces;
+
+import com.baeldung.interfaces.polymorphysim.Circle;
+import com.baeldung.interfaces.polymorphysim.Shape;
+import com.baeldung.interfaces.polymorphysim.Square;
+import org.assertj.core.api.Assertions;
+import org.junit.Test;
+
+public class PolymorphysimUnitTest {
+
+    @Test
+    public void whenInterfacePointsToCircle_CircleAreaMethodisBeingCalled(){
+        double expectedArea = 12.566370614359172;
+        Shape circle = new Circle(2);
+        double actualArea = circle.area();
+        Assertions.assertThat(actualArea).isEqualTo(expectedArea);
+    }
+
+    @Test
+    public void whenInterfacePointsToSquare_SquareAreaMethodisBeingCalled(){
+        double expectedArea = 4;
+        Shape square = new Square(2);
+        double actualArea = square.area();
+        Assertions.assertThat(actualArea).isEqualTo(expectedArea);
+    }
+}