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

02-structural/adapter/StripeClient.java

@@ -0,0 +1,51 @@
+package adapter;
+
+/**
+ * The Adaptee — a third-party payment SDK with a completely different interface.
+ * Imagine this is Stripe's actual SDK: you cannot modify this class,
+ * and it doesn't implement PaymentGateway.
+ *
+ * In real projects, this would be a JAR you depend on.
+ */
+public class StripeClient {
+
+    private final String apiKey;
+
+    public StripeClient(String apiKey) {
+        this.apiKey = apiKey;
+        System.out.println("[Stripe] Initialized with key: " + apiKey.substring(0, 8) + "...");
+    }
+
+    // Stripe uses cents, not decimal amounts
+    public StripeChargeResult createCharge(String customerId, long amountInCents, String currency) {
+        System.out.printf("[Stripe] Charging customer=%s, amount=%d cents, currency=%s%n",
+                customerId, amountInCents, currency);
+        // Simulate success
+        return new StripeChargeResult("ch_" + System.currentTimeMillis(), true, null);
+    }
+
+    // Stripe's refund method takes a charge ID and uses different naming
+    public boolean issueRefund(String chargeId, long amountInCents) {
+        System.out.printf("[Stripe] Refunding charge=%s, amount=%d cents%n", chargeId, amountInCents);
+        return true;
+    }
+
+    // Stripe uses 'retrieve' not 'getStatus', and returns an object
+    public StripeChargeResult retrieveCharge(String chargeId) {
+        System.out.printf("[Stripe] Retrieving charge=%s%n", chargeId);
+        return new StripeChargeResult(chargeId, true, "succeeded");
+    }
+
+    // Stripe-specific result object — nothing in common with your domain
+    public static class StripeChargeResult {
+        public final String chargeId;
+        public final boolean success;
+        public final String status;
+
+        public StripeChargeResult(String chargeId, boolean success, String status) {
+            this.chargeId = chargeId;
+            this.success = success;
+            this.status = status;
+        }
+    }
+}