docs: change the main file to be aling with the subject

subjects/java/checkpoints/factory-blueprint/ExerciseRunner.java

@@ -2,7 +2,20 @@ public class ExerciseRunner {
     public static void main(String[] args) {
         Factory factory = new Factory();
 
-        // Handle invalid product type
+        ConcreteProductA productA = factory.createProduct("A");
+        if (productA != null) {
+            productA.showDetails();
+        } else {
+            System.out.println("Invalid product type");
+        }
+
+        ConcreteProductA productB = factory.createProduct("B");
+        if (productB != null) {
+            productB.showDetails();
+        } else {
+            System.out.println("Invalid product type");
+        }
+
         Object invalidProduct = factory.createProduct("C");
         if (invalidProduct != null) {
             invalidProduct.showDetails();