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/main/java/com/baeldung/interfaces/multiinheritance/Fly.java

@@ -0,0 +1,5 @@
+package com.baeldung.interfaces.multiinheritance;
+
+public abstract interface Fly{
+    void fly();
+}

core-java-8/src/main/java/com/baeldung/interfaces/multiinheritance/Transform.java

@@ -0,0 +1,5 @@
+package com.baeldung.interfaces.multiinheritance;
+
+public interface Transform {
+    void transform();
+}

core-java-8/src/main/java/com/baeldung/interfaces/multiinheritance/Vehicle.java

@@ -0,0 +1,13 @@
+package com.baeldung.interfaces.multiinheritance;
+
+public class Vehicle implements Fly, Transform {
+    @Override
+    public void fly() {
+        System.out.println("I can Fly!!");
+    }
+
+    @Override
+    public void transform() {
+        System.out.println("I can Transform!!");
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/Circle.java

@@ -0,0 +1,21 @@
+package com.baeldung.interfaces.polymorphysim;
+
+public class Circle implements Shape {
+
+    private double radius;
+
+    public Circle(double radius){
+        this.radius = radius;
+    }
+
+    @Override
+    public String name() {
+        return "Circle";
+    }
+
+    @Override
+    public double area() {
+        return Math.PI * (radius * radius);
+    }
+
+}

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/DisplayShape.java

@@ -0,0 +1,22 @@
+package com.baeldung.interfaces.polymorphysim;
+
+import java.util.ArrayList;
+
+public class DisplayShape {
+
+    private ArrayList<Shape> shapes;
+
+    public DisplayShape() {
+        shapes = new ArrayList<>();
+    }
+
+    public void add(Shape shape) {
+        shapes.add(shape);
+    }
+
+    public void display() {
+        for (Shape shape : shapes) {
+            System.out.println(shape.name() + " area: " + shape.area());
+        }
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/MainPolymorphic.java

@@ -0,0 +1,15 @@
+package com.baeldung.interfaces.polymorphysim;
+
+public class MainPolymorphic {
+    public static void main(String[] args){
+
+        Shape circleShape = new Circle(2);
+        Shape squareShape = new Square(2);
+
+        DisplayShape displayShape = new DisplayShape();
+        displayShape.add(circleShape);
+        displayShape.add(squareShape);
+
+        displayShape.display();
+    }
+}

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/Shape.java

@@ -0,0 +1,6 @@
+package com.baeldung.interfaces.polymorphysim;
+
+public interface Shape {
+    public abstract String name();
+    public abstract double area();
+}

core-java-8/src/main/java/com/baeldung/interfaces/polymorphysim/Square.java

@@ -0,0 +1,20 @@
+package com.baeldung.interfaces.polymorphysim;
+
+public class Square implements Shape {
+
+    private double width;
+
+    public Square(double width) {
+        this.width = width;
+    }
+
+    @Override
+    public String name() {
+        return "Square";
+    }
+
+    @Override
+    public double area() {
+        return width * width;
+    }
+}

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);
+    }
+}