Add all 23 GoF design pattern implementations (2026-06-13)

02-structural/adapter/OrderService.java

@@ -0,0 +1,31 @@
+package adapter;
+
+/**
+ * The Client — uses only the PaymentGateway interface.
+ * It has no idea whether it's talking to Stripe, PayPal, or Braintree.
+ * This is the point: the client is completely isolated from the vendor.
+ */
+public class OrderService {
+
+    private final PaymentGateway gateway;
+
+    // Receives a PaymentGateway — could be Stripe, PayPal, anything
+    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.");
+        }
+    }
+}