Add all 23 GoF design pattern implementations

02-structural/adapter/OrderService.java

@@ -0,0 +1,23 @@
+package adapter;
+/**
+ * The Client — uses only the PaymentGateway interface.
+ * It has no idea whether it's talking to Stripe, PayPal, or Braintree.
+ */
+public class OrderService {
+    private final PaymentGateway gateway;
+    public OrderService(PaymentGateway gateway) {
+        this.gateway = gateway;
+    }
+    public void processOrder(String orderId, String customerId, double total) {
+        System.out.printf("%nProcessing order %s for customer %s, total: $%.2f%n",
+                orderId, customerId, total);
+        boolean charged = gateway.charge(customerId, total, "USD");
+        if (charged) {
+            System.out.println("Payment accepted. Order confirmed.");
+            String status = gateway.getStatus("ch_" + orderId);
+            System.out.println("Transaction status: " + status);
+        } else {
+            System.out.println("Payment failed. Order rejected.");
+        }
+    }
+}