add test polymorphism example

src/test/one/A.java

@@ -0,0 +1,7 @@
+package test.one;
+
+public class A implements MyMethodInterface {
+    public void myMethod() {
+
+    }
+}

src/test/one/B.java

@@ -0,0 +1,7 @@
+package test.one;
+
+public class B implements MyMethodInterface {
+    public void myMethod() {
+
+    }
+}

src/test/one/Main.java

@@ -0,0 +1,13 @@
+package test.one;
+
+public class Main {
+    public static void main(String[] args) {
+        Object[] objects = {
+                new A(),
+                new B(),
+        };
+        for (Object object : objects) {
+            ((MyMethodInterface)object).myMethod();
+        }
+    }
+}

src/test/one/MyMethodInterface.java

@@ -0,0 +1,5 @@
+package test.one;
+
+public interface MyMethodInterface {
+    void myMethod();
+}