Add all 23 GoF design pattern implementations

01-creational/abstract-factory/Application.java

@@ -0,0 +1,30 @@
+package abstractfactory;
+
+public class Application {
+
+    // The client holds references to the Abstract Factory and Abstract Products.
+    // It never imports LightButton, DarkButton, or any concrete class.
+    private final UIFactory factory;
+    private Button submitButton;
+    private TextField usernameField;
+
+    public Application(UIFactory factory) {
+        this.factory = factory;  // theme is injected; client doesn't decide
+    }
+
+    public void buildUI() {
+        // Ask the factory — get consistent products from the same family
+        submitButton = factory.createButton();
+        usernameField = factory.createTextField();
+    }
+
+    public void render() {
+        System.out.println("Rendering login screen:");
+        usernameField.render();
+        submitButton.render();
+    }
+
+    public void simulateSubmit() {
+        submitButton.onClick();
+    }
+}