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

02-structural/proxy/Main.java

@@ -0,0 +1,51 @@
+package proxy;
+
+/**
+ * Proxy Design Pattern — Runnable Demo
+ *
+ * Shows two proxy types:
+ *  1. Virtual Proxy (lazy connection)
+ *  2. Logging Proxy (cross-cutting concern)
+ *  3. Proxy chaining (both together)
+ *
+ * Run: javac proxy/*.java && java proxy.Main
+ * Article: https://ankurm.com/proxy-design-pattern-java/
+ */
+public class Main {
+
+    public static void main(String[] args) throws InterruptedException {
+        System.out.println("=== Proxy Design Pattern Demo ===\n");
+
+        // --- Virtual Proxy: lazy connection ---
+        System.out.println("-- Virtual Proxy (lazy loading) --");
+        DatabaseConnection lazy = new LazyConnectionProxy("jdbc:postgresql://localhost/mydb");
+        lazy.connect();  // absorbed by proxy, no real connection yet
+        System.out.println("(no real connection yet — saved startup time)");
+        System.out.println("Result: " + lazy.executeQuery("SELECT * FROM users WHERE id=1"));
+        System.out.println("Result: " + lazy.executeQuery("SELECT COUNT(*) FROM orders"));
+        lazy.disconnect();
+
+        System.out.println();
+
+        // --- Logging Proxy: wraps the real connection ---
+        System.out.println("-- Logging Proxy --");
+        DatabaseConnection real = new RealDatabaseConnection("jdbc:mysql://localhost/shopdb");
+        real.connect();
+        DatabaseConnection logged = new LoggingProxy(real);
+        logged.executeQuery("SELECT * FROM products LIMIT 10");
+        logged.disconnect();
+
+        System.out.println();
+
+        // --- Proxy chaining: lazy + logging ---
+        System.out.println("-- Chained Proxies: Lazy + Logging --");
+        DatabaseConnection chain =
+            new LoggingProxy(
+                new LazyConnectionProxy("jdbc:oracle://localhost/warehouse"));
+        chain.connect();
+        chain.executeQuery("SELECT SUM(quantity) FROM inventory");
+        chain.disconnect();
+
+        System.out.println("\n=== Demo complete ===");
+    }
+}