add test code from discussion after lecture

src/test/Main.java

@@ -0,0 +1,15 @@
+package test;
+
+public class Main {
+    public static void main(String[] args) {
+        A a = new A();
+        System.out.println(a.getF());
+        a.setF(1);
+        System.out.println(a.getF());
+
+        System.out.println(a.f);
+
+        int[] array = {1, 2, 1};
+        System.out.println(array.length);
+    }
+}