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

03-behavioral/state/Main.java

@@ -0,0 +1,26 @@
+package state;
+
+/**
+ * State Design Pattern — Runnable Demo
+ * Run: javac state/*.java -d out/state && java -cp out/state state.Main
+ * Article: https://ankurm.com/state-design-pattern-java/
+ */
+public class Main {
+    public static void main(String[] args) {
+        System.out.println("=== State Design Pattern Demo ===\n");
+
+        TrafficLight light = new TrafficLight();
+        System.out.println("Starting state: " + light.getColor());
+
+        System.out.println("\n-- Cycling through states --");
+        for (int i = 0; i < 6; i++) {
+            light.next();
+        }
+
+        System.out.println("\n-- Without State pattern: a single class with if/else --");
+        System.out.println("   Every new state adds to every method's if-else chain.");
+        System.out.println("   With State: add one new class, touch nothing else.");
+
+        System.out.println("\n=== Demo complete ===");
+    }
+}