Add all 23 GoF design pattern implementations

02-structural/adapter/Main.java

@@ -0,0 +1,27 @@
+package adapter;
+
+public class Main {
+
+    public static void main(String[] args) {
+        System.out.println("=== Adapter Design Pattern Demo ===\n");
+
+        // --- Object Adapter: Stripe ---
+        System.out.println("-- Using Stripe via Adapter --");
+        StripeClient stripeClient = new StripeClient("sk_test_4eC39HqLyjWDarjtT1zdp7dc");
+        PaymentGateway stripeGateway = new StripePaymentAdapter(stripeClient);
+
+        OrderService orderService = new OrderService(stripeGateway);
+        orderService.processOrder("ORD-001", "cus_abc123", 99.99);
+
+        System.out.println("\n-- Testing refund --");
+        boolean refunded = stripeGateway.refund("ch_ORD-001", 99.99);
+        System.out.println("Refund issued: " + refunded);
+
+        // --- JDK Example: InputStreamReader as Adapter ---
+        System.out.println("\n-- JDK Adapter: InputStreamReader --");
+        System.out.println("InputStreamReader wraps System.in (InputStream) as a Reader.");
+        System.out.println("Your code reads chars; the adapter handles byte-to-char conversion.");
+
+        System.out.println("\n=== Demo complete ===");
+    }
+}