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

02-structural/proxy/LazyConnectionProxy.java

@@ -0,0 +1,52 @@
+package proxy;
+
+/**
+ * Virtual Proxy — delays creating the RealDatabaseConnection until
+ * the first actual query is made. If no query is ever made (e.g.,
+ * the service is initialized but never used in this request),
+ * the expensive connection is never opened.
+ *
+ * This is exactly how Hibernate proxies work: entities are not
+ * loaded from the database until you access a field on them.
+ */
+public class LazyConnectionProxy implements DatabaseConnection {
+
+    private final String url;
+    private RealDatabaseConnection real;  // null until first use
+
+    public LazyConnectionProxy(String url) {
+        this.url = url;
+        System.out.println("[Proxy] Created for " + url + " (real connection NOT opened yet)");
+    }
+
+    // Lazy initialization — create and connect only on first real need
+    private void initIfNeeded() {
+        if (real == null) {
+            System.out.println("[Proxy] First access — initializing real connection...");
+            real = new RealDatabaseConnection(url);
+            real.connect();
+        }
+    }
+
+    @Override
+    public void connect() {
+        // Proxy absorbs the connect() call — real connection opened lazily
+        System.out.println("[Proxy] connect() called — deferring to first query");
+    }
+
+    @Override
+    public String executeQuery(String sql) {
+        initIfNeeded();  // NOW we actually need the connection
+        return real.executeQuery(sql);
+    }
+
+    @Override
+    public void disconnect() {
+        if (real != null) {
+            real.disconnect();
+            real = null;
+        } else {
+            System.out.println("[Proxy] disconnect() called but connection was never opened");
+        }
+    }
+}