Add all 23 GoF design pattern implementations

02-structural/adapter/StripePaymentAdapter.java

@@ -0,0 +1,36 @@
+package adapter;
+/**
+ * The Adapter — bridges StripeClient to PaymentGateway.
+ *
+ * Object Adapter variant: holds a StripeClient instance via composition.
+ * This means it can wrap any StripeClient including subclasses.
+ */
+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 1: dollars → cents
+        long amountInCents = Math.round(amount * 100);
+        // Translation 2: charge() → createCharge(), lowercase currency
+        StripeClient.StripeChargeResult result =
+                stripe.createCharge(customerId, amountInCents, currency.toLowerCase());
+        // Translation 3: StripeChargeResult → boolean
+        return result.success;
+    }
+    @Override
+    public boolean refund(String transactionId, double amount) {
+        long amountInCents = Math.round(amount * 100);
+        // Translation: refund() → issueRefund(), your "transactionId" is Stripe's "chargeId"
+        return stripe.issueRefund(transactionId, amountInCents);
+    }
+    @Override
+    public String getStatus(String transactionId) {
+        // Translation: getStatus() → retrieveCharge(), StripeChargeResult → String
+        StripeClient.StripeChargeResult result = stripe.retrieveCharge(transactionId);
+        if (!result.success) return "FAILED";
+        return result.status != null ? result.status.toUpperCase() : "UNKNOWN";
+    }
+}