Add all 23 GoF design pattern implementations

02-structural/adapter/README.md

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+# Adapter Design Pattern — Java Example
+
+**Pattern:** Structural → Adapter
+**Article:** https://ankurm.com/adapter-design-pattern-java/
+
+## What this example shows
+
+Wraps a third-party `StripeClient` (with its own API) behind a `PaymentGateway` interface that your application code expects. The `OrderService` client never touches `StripeClient` directly — it only sees `PaymentGateway`. Swapping payment providers requires changing one line.
+
+## How to run
+
+```bash
+# From this folder:
+javac adapter/*.java
+java adapter.Main
+```
+
+Requires Java 25.
+
+## Files
+
+| Post Section | File(s) |
+|---|---|
+| Step 1 — Define the Target Interface | `PaymentGateway.java` |
+| Step 2 — The Adaptee (What You're Wrapping) | `StripeClient.java` |
+| Step 3 — The Object Adapter | `StripePaymentAdapter.java` |
+| Step 4 — The Client (Knows Nothing About Stripe) | `OrderService.java` |
+| Putting It Together: The Main Demo | `Main.java` |
+| Object Adapter vs Class Adapter | `StripePaymentClassAdapter.java` |
+
+Note: the `InputStreamReader` JDK-adapter snippet is illustrative only — it is not part of this repository's runnable example.
+
+## See Also
+
+- Full article: https://ankurm.com/adapter-design-pattern-java/
+- All design patterns: https://ankurm.com/design-patterns-java/