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

02-structural/adapter/StripePaymentAdapter.java

@@ -0,0 +1,44 @@
+package adapter;
+
+/**
+ * The Adapter — bridges StripeClient (Adaptee) to PaymentGateway (Target).
+ *
+ * This is the Object Adapter variant: it holds a StripeClient instance
+ * via composition (not inheritance), so it can adapt any StripeClient
+ * including subclasses.
+ *
+ * The key responsibility: translate YOUR interface's methods into
+ * calls that Stripe understands — data conversion included.
+ */
+public class StripePaymentAdapter implements PaymentGateway {
+
+    private final StripeClient stripe;
+
+    public StripePaymentAdapter(StripeClient stripe) {
+        this.stripe = stripe;
+    }
+
+    @Override
+    public boolean charge(String customerId, double amount, String currency) {
+        // Translation: your code uses decimal dollars; Stripe wants integer cents
+        long amountInCents = Math.round(amount * 100);
+        StripeClient.StripeChargeResult result =
+                stripe.createCharge(customerId, amountInCents, currency.toLowerCase());
+        return result.success;
+    }
+
+    @Override
+    public boolean refund(String transactionId, double amount) {
+        // Translation: your "transactionId" is Stripe's "chargeId"
+        long amountInCents = Math.round(amount * 100);
+        return stripe.issueRefund(transactionId, amountInCents);
+    }
+
+    @Override
+    public String getStatus(String transactionId) {
+        // Translation: map Stripe's object to your simple status string
+        StripeClient.StripeChargeResult result = stripe.retrieveCharge(transactionId);
+        if (!result.success) return "FAILED";
+        return result.status != null ? result.status.toUpperCase() : "UNKNOWN";
+    }
+}