Sync Factory Method, Abstract Factory, Builder, Prototype to Java 25; fix post/code mismatches

01-creational/abstract-factory/Application.java

@@ -1,21 +1,30 @@
 package abstractfactory;
 
-/** Client - uses the factory without knowing concrete classes */
 public class Application {
-    private final Button button;
-    private final Checkbox checkbox;
 
-    public Application(GUIFactory factory) {
+    // The client holds references to the Abstract Factory and Abstract Products.
-        button   = factory.createButton();
+    // It never imports LightButton, DarkButton, or any concrete class.
-        checkbox = factory.createCheckbox();
+    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() {
-        button.render();
+        System.out.println("Rendering login screen:");
-        checkbox.render();
+        usernameField.render();
+        submitButton.render();
     }
 
-    public void simulateClick() {
+    public void simulateSubmit() {
-        button.onClick();
+        submitButton.onClick();
     }
 }

01-creational/abstract-factory/Button.java

@@ -1,6 +1,7 @@
 package abstractfactory;
 
+// Every button, regardless of theme, must be able to render and handle clicks
 public interface Button {
-    void render();
+    void render();   // draw on screen
-    void onClick();
+    void onClick();  // respond to a click event
 }

01-creational/abstract-factory/Checkbox.java

@@ -1,5 +0,0 @@
-package abstractfactory;
-
-public interface Checkbox {
-    void render();
-}

01-creational/abstract-factory/DarkButton.java

@@ -0,0 +1,11 @@
+package abstractfactory;
+public class DarkButton implements Button {
+    @Override
+    public void render() {
+        System.out.println("[Dark Button] Charcoal background, white text, no border");
+    }
+    @Override
+    public void onClick() {
+        System.out.println("[Dark Button] Bright highlight ripple effect");
+    }
+}

01-creational/abstract-factory/DarkTextField.java

@@ -0,0 +1,10 @@
+package abstractfactory;
+public class DarkTextField implements TextField {
+    private String value = "";
+    @Override
+    public void render() {
+        System.out.println("[Dark TextField] Dark gray background, light placeholder text");
+    }
+    @Override
+    public String getValue() { return value; }
+}

01-creational/abstract-factory/DarkThemeFactory.java

@@ -0,0 +1,14 @@
+package abstractfactory;
+
+public class DarkThemeFactory implements UIFactory {
+
+    @Override
+    public Button createButton() {
+        return new DarkButton();        // Only Dark products come from this factory
+    }
+
+    @Override
+    public TextField createTextField() {
+        return new DarkTextField();
+    }
+}

01-creational/abstract-factory/GUIFactory.java

@@ -1,7 +0,0 @@
-package abstractfactory;
-
-/** Abstract Factory - creates families of related UI components */
-public interface GUIFactory {
-    Button createButton();
-    Checkbox createCheckbox();
-}

01-creational/abstract-factory/LightButton.java

@@ -0,0 +1,11 @@
+package abstractfactory;
+public class LightButton implements Button {
+    @Override
+    public void render() {
+        System.out.println("[Light Button] White background, dark text, 1px gray border");
+    }
+    @Override
+    public void onClick() {
+        System.out.println("[Light Button] Subtle gray ripple effect");
+    }
+}

01-creational/abstract-factory/LightTextField.java

@@ -0,0 +1,10 @@
+package abstractfactory;
+public class LightTextField implements TextField {
+    private String value = "";
+    @Override
+    public void render() {
+        System.out.println("[Light TextField] White background, dark placeholder text");
+    }
+    @Override
+    public String getValue() { return value; }
+}

01-creational/abstract-factory/LightThemeFactory.java

@@ -0,0 +1,14 @@
+package abstractfactory;
+
+public class LightThemeFactory implements UIFactory {
+
+    @Override
+    public Button createButton() {
+        return new LightButton();       // Only Light products come from this factory
+    }
+
+    @Override
+    public TextField createTextField() {
+        return new LightTextField();
+    }
+}

01-creational/abstract-factory/MacButton.java

@@ -1,6 +0,0 @@
-package abstractfactory;
-
-public class MacButton implements Button {
-    @Override public void render()   { System.out.println("[Mac] Rendering button with rounded corners"); }
-    @Override public void onClick()  { System.out.println("[Mac] Button clicked - glow animation"); }
-}

01-creational/abstract-factory/MacCheckbox.java

@@ -1,5 +0,0 @@
-package abstractfactory;
-
-public class MacCheckbox implements Checkbox {
-    @Override public void render() { System.out.println("[Mac] Rendering checkbox with rounded tick box"); }
-}

01-creational/abstract-factory/MacFactory.java

@@ -1,6 +0,0 @@
-package abstractfactory;
-
-public class MacFactory implements GUIFactory {
-    @Override public Button   createButton()   { return new MacButton(); }
-    @Override public Checkbox createCheckbox() { return new MacCheckbox(); }
-}

01-creational/abstract-factory/Main.java

@@ -1,22 +1,16 @@
 package abstractfactory;
 
+// Entry point: the ONLY place that knows the theme
 public class Main {
     public static void main(String[] args) {
-        System.out.println("=== Abstract Factory Pattern Demo ===\n");
 
-        String os = System.getProperty("os.name", "Windows").toLowerCase();
+        // Production: read theme from config or OS preference
-        GUIFactory factory = os.contains("mac") ? new MacFactory() : new WindowsFactory();
+        String theme = System.getProperty("app.theme", "light");
-
+        UIFactory factory = "dark".equals(theme) ? new DarkThemeFactory() : new LightThemeFactory();
-        System.out.println("Detected OS family: " + (os.contains("mac") ? "Mac" : "Windows"));
-        System.out.println();
 
         Application app = new Application(factory);
+        app.buildUI();
         app.render();
-        app.simulateClick();
+        app.simulateSubmit();
-
-        System.out.println("\n--- Forcing Mac UI ---");
-        Application macApp = new Application(new MacFactory());
-        macApp.render();
-        macApp.simulateClick();
     }
 }

01-creational/abstract-factory/TextField.java

@@ -0,0 +1,7 @@
+package abstractfactory;
+
+// Every text field must be able to render and return its value
+public interface TextField {
+    void render();
+    String getValue();
+}

01-creational/abstract-factory/UIFactory.java

@@ -0,0 +1,13 @@
+package abstractfactory;
+
+public interface UIFactory {
+
+    // Factory method for buttons — returns the abstract type, not LightButton or DarkButton
+    Button createButton();
+
+    // Factory method for text fields — same principle
+    TextField createTextField();
+
+    // Adding a new product type (e.g., Checkbox) means adding a method here
+    // AND implementing it in every Concrete Factory. This is the one cost of the pattern.
+}

01-creational/abstract-factory/WindowsButton.java

@@ -1,6 +0,0 @@
-package abstractfactory;
-
-public class WindowsButton implements Button {
-    @Override public void render()   { System.out.println("[Windows] Rendering button with square corners"); }
-    @Override public void onClick()  { System.out.println("[Windows] Button clicked - raised border effect"); }
-}

01-creational/abstract-factory/WindowsCheckbox.java

@@ -1,5 +0,0 @@
-package abstractfactory;
-
-public class WindowsCheckbox implements Checkbox {
-    @Override public void render() { System.out.println("[Windows] Rendering checkbox with square tick box"); }
-}

01-creational/abstract-factory/WindowsFactory.java

@@ -1,6 +0,0 @@
-package abstractfactory;
-
-public class WindowsFactory implements GUIFactory {
-    @Override public Button   createButton()   { return new WindowsButton(); }
-    @Override public Checkbox createCheckbox() { return new WindowsCheckbox(); }
-}

01-creational/builder/Director.java

@@ -1,12 +0,0 @@
-package builder;
-
-/** Director knows how to build common configurations */
-public class Director {
-    public House buildStarter(House.Builder builder) {
-        return builder.rooms(2).floors(1).garage(false).roofType("gabled").build();
-    }
-
-    public House buildLuxury(House.Builder builder) {
-        return builder.rooms(6).floors(3).garage(true).garden(true).pool(true).roofType("hip").build();
-    }
-}

01-creational/builder/House.java

@@ -1,43 +0,0 @@
-package builder;
-
-public class House {
-    private final int rooms;
-    private final int floors;
-    private final boolean hasGarage;
-    private final boolean hasGarden;
-    private final boolean hasPool;
-    private final String roofType;
-
-    private House(Builder builder) {
-        this.rooms     = builder.rooms;
-        this.floors    = builder.floors;
-        this.hasGarage = builder.hasGarage;
-        this.hasGarden = builder.hasGarden;
-        this.hasPool   = builder.hasPool;
-        this.roofType  = builder.roofType;
-    }
-
-    @Override
-    public String toString() {
-        return "House{rooms=" + rooms + ", floors=" + floors
-                + ", garage=" + hasGarage + ", garden=" + hasGarden
-                + ", pool=" + hasPool + ", roof='" + roofType + "'}";
-    }
-
-    public static class Builder {
-        private int rooms = 1;
-        private int floors = 1;
-        private boolean hasGarage = false;
-        private boolean hasGarden = false;
-        private boolean hasPool   = false;
-        private String roofType   = "flat";
-
-        public Builder rooms(int rooms)           { this.rooms = rooms;         return this; }
-        public Builder floors(int floors)         { this.floors = floors;       return this; }
-        public Builder garage(boolean v)          { this.hasGarage = v;         return this; }
-        public Builder garden(boolean v)          { this.hasGarden = v;         return this; }
-        public Builder pool(boolean v)            { this.hasPool = v;           return this; }
-        public Builder roofType(String roofType)  { this.roofType = roofType;   return this; }
-        public House build()                      { return new House(this); }
-    }
-}

01-creational/builder/HttpClientConfig.java

@@ -0,0 +1,27 @@
+package builder;
+
+public class HttpClientConfig {
+
+    // Director method 1: a health check probe — short timeout, no retries
+    public HttpRequest buildHealthCheck(String baseUrl) {
+        return new HttpRequest.Builder()
+            .url(baseUrl + "/health")
+            .method("GET")
+            .timeoutMs(2_000)     // fast fail for health checks
+            .maxRetries(0)
+            .build();
+    }
+
+    // Director method 2: a resilient POST with standard JSON headers and retries
+    public HttpRequest buildResilientPost(String url, String jsonBody) {
+        return new HttpRequest.Builder()
+            .url(url)
+            .method("POST")
+            .body(jsonBody)
+            .header("Content-Type", "application/json")
+            .header("Accept", "application/json")
+            .timeoutMs(15_000)
+            .maxRetries(3)
+            .build();
+    }
+}

01-creational/builder/HttpRequest.java

@@ -0,0 +1,76 @@
+package builder;
+
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.Map;
+import java.util.Objects;
+
+public final class HttpRequest {
+
+    // All fields are final: the object is immutable after build() returns.
+    private final String url;
+    private final String method;
+    private final String body;
+    private final Map<String, String> headers;
+    private final int timeoutMs;
+    private final int maxRetries;
+
+    // Private: the only path to an HttpRequest is through Builder.build()
+    private HttpRequest(Builder builder) {
+        this.url        = Objects.requireNonNull(builder.url, "URL is required");
+        this.method     = builder.method;
+        this.body       = builder.body;
+        this.headers    = Collections.unmodifiableMap(new HashMap<>(builder.headers));
+        this.timeoutMs  = builder.timeoutMs;
+        this.maxRetries = builder.maxRetries;
+    }
+
+    // Getters only — no setters, enforcing immutability
+    public String getUrl()          { return url; }
+    public String getMethod()       { return method; }
+    public String getBody()         { return body; }
+    public Map<String, String> getHeaders() { return headers; }
+    public int getTimeoutMs()       { return timeoutMs; }
+    public int getMaxRetries()      { return maxRetries; }
+
+    @Override
+    public String toString() {
+        return String.format("%s %s (timeout=%dms, retries=%d, headers=%s, body=%s)",
+            method, url, timeoutMs, maxRetries, headers, body);
+    }
+
+    // -----------------------------------------------------------------------
+    // THE BUILDER — static inner class so it can call the private constructor
+    // -----------------------------------------------------------------------
+    public static class Builder {
+
+        // Required field — no default, must be set
+        private String url;
+
+        // Optional fields with sensible defaults
+        private String method     = "GET";
+        private String body       = null;
+        private Map<String, String> headers = new HashMap<>();
+        private int timeoutMs     = 30_000;  // 30 seconds
+        private int maxRetries    = 0;
+
+        // Fluent methods: each returns 'this' so calls can be chained
+        public Builder url(String url)              { this.url = url; return this; }
+        public Builder method(String method)        { this.method = method; return this; }
+        public Builder body(String body)            { this.body = body; return this; }
+        public Builder header(String key, String v) { headers.put(key, v); return this; }
+        public Builder timeoutMs(int ms)            { this.timeoutMs = ms; return this; }
+        public Builder maxRetries(int n)            { this.maxRetries = n; return this; }
+
+        // Terminal method: validates and creates the immutable HttpRequest
+        public HttpRequest build() {
+            if (url == null || url.isBlank()) {
+                throw new IllegalStateException("url() is required before calling build()");
+            }
+            if (maxRetries < 0) {
+                throw new IllegalStateException("maxRetries must be >= 0");
+            }
+            return new HttpRequest(this);  // calls the private constructor
+        }
+    }
+}

01-creational/builder/Main.java

@@ -1,20 +1,42 @@
 package builder;
 
 public class Main {
+
     public static void main(String[] args) {
-        System.out.println("=== Builder Pattern Demo ===\n");
 
-        Director director = new Director();
+        // Simple GET — only the required field
+        HttpRequest ping = new HttpRequest.Builder()
+            .url("https://api.example.com/health")
+            .build();
 
-        House starter = director.buildStarter(new House.Builder());
+        System.out.println("Simple GET: " + ping);
-        System.out.println("Starter home : " + starter);
 
-        House luxury = director.buildLuxury(new House.Builder());
+        // Full POST with authentication and retry
-        System.out.println("Luxury home  : " + luxury);
+        HttpRequest post = new HttpRequest.Builder()
+            .url("https://api.example.com/orders")
+            .method("POST")
+            .body("{\"item\":\"book\",\"qty\":1}")
+            .header("Content-Type", "application/json")
+            .header("Authorization", "Bearer eyJ...")
+            .timeoutMs(10_000)   // 10 seconds — name is self-documenting
+            .maxRetries(3)
+            .build();
 
-        // Client builds a custom house directly without the Director
+        System.out.println("POST: " + post);
-        House custom = new House.Builder()
+
-                .rooms(4).floors(2).garden(true).roofType("mansard").build();
+        // build() throws if url is missing — validation at construction time
-        System.out.println("Custom home  : " + custom);
+        try {
+            HttpRequest bad = new HttpRequest.Builder().build(); // no URL!
+        } catch (IllegalStateException e) {
+            System.out.println("Caught: " + e.getMessage()); // url() is required
+        }
+
+        // Using the Director for the two standard presets defined above
+        HttpClientConfig config = new HttpClientConfig();
+        HttpRequest healthCheck = config.buildHealthCheck("https://api.example.com");
+        System.out.println("Health check: " + healthCheck);
+
+        HttpRequest order = config.buildResilientPost("https://api.example.com/orders", "{\"qty\":1}");
+        System.out.println("Order: " + order);
     }
 }

01-creational/factory-method/EmailNotification.java

@@ -1,11 +1,13 @@
 package factorymethod;
 
 public class EmailNotification implements Notification {
-    private final String email;
-    public EmailNotification(String email) { this.email = email; }
 
     @Override
-    public void send(String message) {
+    public void send(String recipient, String message) {
-        System.out.println("Email -> " + email + ": " + message);
+        // In production: use JavaMail or Spring Mail
+        System.out.printf("  [EMAIL] To: %s | Body: %s%n", recipient, message);
     }
+
+    @Override
+    public String getType() { return "EMAIL"; }
 }

01-creational/factory-method/EmailSender.java

@@ -0,0 +1,8 @@
+package factorymethod;
+
+public class EmailSender extends NotificationSender {
+    @Override
+    protected Notification createNotification() {
+        return new EmailNotification();
+    }
+}

01-creational/factory-method/EmailService.java

@@ -1,11 +0,0 @@
-package factorymethod;
-
-public class EmailService extends NotificationService {
-    private final String email;
-    public EmailService(String email) { this.email = email; }
-
-    @Override
-    protected Notification createNotification() {
-        return new EmailNotification(email);
-    }
-}

01-creational/factory-method/Main.java

@@ -1,17 +1,23 @@
 package factorymethod;
 
 public class Main {
+
     public static void main(String[] args) {
-        System.out.println("=== Factory Method Pattern Demo ===\n");
 
-        NotificationService[] services = {
+        // The client only knows about NotificationSender (the Creator)
-            new EmailService("alice@example.com"),
+        NotificationSender sender;
-            new SmsService("+1-555-0123"),
-            new PushService("device-token-abc123")
-        };
 
-        for (NotificationService service : services) {
+        sender = new EmailSender();
-            service.notifyUser("Your order #1042 has been shipped!");
+        sender.notify("alice@example.com", "Your order has shipped!");
-        }
+
+        sender = new SmsSender();
+        sender.notify("+1-555-0100", "OTP: 482910");
+
+        sender = new PushSender();
+        sender.notify("device-token-xyz", "New message from Bob");
+
+        // Adding Slack: just swap the creator. Client code doesn't change.
+        sender = new SlackSender();  // new class, nothing else touched
+        sender.notify("#alerts", "CPU usage above 90%");
     }
 }

01-creational/factory-method/Notification.java

@@ -1,5 +1,11 @@
 package factorymethod;
 
 public interface Notification {
-    void send(String message);
+
+    // Every notification must know how to deliver itself
+    void send(String recipient, String message);
+
+    // Used by the Creator for logging — it needs to know the type
+    // without knowing the concrete class
+    String getType();
 }

01-creational/factory-method/NotificationSender.java

@@ -0,0 +1,31 @@
+package factorymethod;
+
+public abstract class NotificationSender {
+
+    // THE factory method — this is the one thing subclasses override.
+    // It returns a Notification (the Product interface), never a concrete class.
+    protected abstract Notification createNotification();
+
+    // The shared workflow — marked final so subclasses cannot change it.
+    // It calls createNotification() to get the right notification,
+    // then runs the same steps every time regardless of which channel was created.
+    public final void notify(String recipient, String message) {
+        Notification notification = createNotification();     // delegate creation
+        System.out.println("Sending " + notification.getType() + " notification...");
+        notification.send(recipient, message);                // use the Product interface
+        System.out.println("Delivered.");
+    }
+
+    // Shared retry logic — works for all channels without change
+    public void notifyWithRetry(String recipient, String message, int maxRetries) {
+        for (int attempt = 1; attempt <= maxRetries; attempt++) {
+            try {
+                notify(recipient, message);
+                return; // success — exit
+            } catch (Exception e) {
+                System.err.printf("Attempt %d failed: %s%n", attempt, e.getMessage());
+            }
+        }
+        throw new RuntimeException("All " + maxRetries + " attempts failed");
+    }
+}

01-creational/factory-method/NotificationService.java

@@ -1,11 +1,24 @@
 package factorymethod;
 
-/** Creator - declares the factory method */
+public class NotificationService {
-public abstract class NotificationService {
-    protected abstract Notification createNotification();
 
-    public void notifyUser(String message) {
+    public void send(String type, String recipient, String message) {
-        Notification n = createNotification();
+
-        n.send(message);
+        // Creation logic mixed with business logic
+        Notification notification;
+        if ("EMAIL".equals(type)) {
+            notification = new EmailNotification();
+        } else if ("SMS".equals(type)) {
+            notification = new SmsNotification();
+        } else if ("PUSH".equals(type)) {
+            notification = new PushNotification();
+        } else {
+            throw new IllegalArgumentException("Unknown type: " + type);
+        }
+
+        // Business logic that should never change
+        System.out.println("Sending " + type + " to " + recipient);
+        notification.send(recipient, message);
+        System.out.println("Delivered.");
     }
 }

01-creational/factory-method/PushNotification.java

@@ -1,11 +1,13 @@
 package factorymethod;
 
 public class PushNotification implements Notification {
-    private final String deviceToken;
-    public PushNotification(String deviceToken) { this.deviceToken = deviceToken; }
 
     @Override
-    public void send(String message) {
+    public void send(String recipient, String message) {
-        System.out.println("Push -> " + deviceToken + ": " + message);
+        // In production: use Firebase FCM
+        System.out.printf("  [PUSH]  To: %s | Alert: %s%n", recipient, message);
     }
+
+    @Override
+    public String getType() { return "PUSH"; }
 }

01-creational/factory-method/PushSender.java

@@ -0,0 +1,8 @@
+package factorymethod;
+
+public class PushSender extends NotificationSender {
+    @Override
+    protected Notification createNotification() {
+        return new PushNotification();
+    }
+}

01-creational/factory-method/PushService.java

@@ -1,11 +0,0 @@
-package factorymethod;
-
-public class PushService extends NotificationService {
-    private final String token;
-    public PushService(String token) { this.token = token; }
-
-    @Override
-    protected Notification createNotification() {
-        return new PushNotification(token);
-    }
-}

01-creational/factory-method/SlackNotification.java

@@ -0,0 +1,11 @@
+package factorymethod;
+
+// New Concrete Product — knows how to send to Slack
+public class SlackNotification implements Notification {
+    @Override
+    public void send(String recipient, String message) {
+        System.out.printf("  [SLACK] Channel: %s | Message: %s%n", recipient, message);
+    }
+    @Override
+    public String getType() { return "SLACK"; }
+}

01-creational/factory-method/SlackSender.java

@@ -0,0 +1,9 @@
+package factorymethod;
+
+// New Concrete Creator — knows to create a SlackNotification
+public class SlackSender extends NotificationSender {
+    @Override
+    protected Notification createNotification() {
+        return new SlackNotification();
+    }
+}

01-creational/factory-method/SmsNotification.java

@@ -1,11 +1,13 @@
 package factorymethod;
 
 public class SmsNotification implements Notification {
-    private final String phone;
-    public SmsNotification(String phone) { this.phone = phone; }
 
     @Override
-    public void send(String message) {
+    public void send(String recipient, String message) {
-        System.out.println("SMS -> " + phone + ": " + message);
+        // In production: use Twilio SDK
+        System.out.printf("  [SMS]   To: %s | Text: %s%n", recipient, message);
     }
+
+    @Override
+    public String getType() { return "SMS"; }
 }

01-creational/factory-method/SmsSender.java

@@ -0,0 +1,8 @@
+package factorymethod;
+
+public class SmsSender extends NotificationSender {
+    @Override
+    protected Notification createNotification() {
+        return new SmsNotification();
+    }
+}

01-creational/factory-method/SmsService.java

@@ -1,11 +0,0 @@
-package factorymethod;
-
-public class SmsService extends NotificationService {
-    private final String phone;
-    public SmsService(String phone) { this.phone = phone; }
-
-    @Override
-    protected Notification createNotification() {
-        return new SmsNotification(phone);
-    }
-}

01-creational/prototype/Circle.java

@@ -1,24 +0,0 @@
-package prototype;
-
-public class Circle extends Shape {
-    private int radius;
-
-    public Circle(int radius, String color) {
-        this.radius = radius;
-        this.color  = color;
-    }
-
-    /** Copy constructor used by clone() */
-    private Circle(Circle source) {
-        super(source);
-        this.radius = source.radius;
-    }
-
-    @Override
-    public Circle clone() { return new Circle(this); }
-
-    @Override
-    public String toString() {
-        return "Circle{color=" + color + ", radius=" + radius + ", pos=(" + x + "," + y + ")}";
-    }
-}

01-creational/prototype/Copyable.java

@@ -0,0 +1,8 @@
+package prototype;
+
+// Our Prototype interface: any class that can clone itself implements this.
+// The return type T allows each implementing class to return its own type,
+// not the raw interface type, which makes the client code cleaner.
+public interface Copyable<T> {
+    T copy();
+}

01-creational/prototype/Document.java

@@ -0,0 +1,46 @@
+package prototype;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+
+public class Document implements Copyable<Document> {
+
+    private String title;                // String: immutable, safe to share on copy
+    private String content;             // String: immutable, safe to share on copy
+    private List<String> tags;          // List: mutable, MUST be deep-copied
+    private DocumentMetadata metadata;  // Mutable object, MUST be deep-copied
+
+    public Document(String title, String content, List<String> tags, DocumentMetadata metadata) {
+        this.title    = title;
+        this.content  = content;
+        this.tags     = new ArrayList<>(tags); // defensive copy on construction
+        this.metadata = metadata;
+    }
+
+    // Copy constructor: the preferred Prototype implementation in modern Java
+    public Document(Document source) {
+        this.title    = source.title;                    // immutable: share
+        this.content  = source.content;                 // immutable: share
+        this.tags     = new ArrayList<>(source.tags);  // mutable: new list
+        this.metadata = source.metadata.copy();         // mutable: deep copy via Copyable
+    }
+
+    @Override
+    public Document copy() {
+        return new Document(this); // delegates to copy constructor
+    }
+
+    // Getters and setters
+    public String getTitle()               { return title; }
+    public void setTitle(String title)     { this.title = title; }
+    public String getContent()             { return content; }
+    public void setContent(String content) { this.content = content; }
+    public List<String> getTags()          { return Collections.unmodifiableList(tags); }
+    public void addTag(String tag)         { tags.add(tag); }
+    public DocumentMetadata getMetadata()  { return metadata; }
+
+    @Override public String toString() {
+        return String.format("Document{title='%s', tags=%s, %s}", title, tags, metadata);
+    }
+}

01-creational/prototype/DocumentMetadata.java

@@ -0,0 +1,39 @@
+package prototype;
+
+import java.time.LocalDate;
+
+public class DocumentMetadata implements Copyable<DocumentMetadata> {
+
+    private String author;
+    private LocalDate createdDate; // LocalDate is immutable — safe to share
+    private String version;
+
+    public DocumentMetadata(String author, LocalDate createdDate, String version) {
+        this.author = author;
+        this.createdDate = createdDate; // safe: LocalDate is immutable
+        this.version = version;
+    }
+
+    // Copy constructor: creates a new instance with the same values
+    public DocumentMetadata(DocumentMetadata source) {
+        this.author      = source.author;      // String: immutable, safe to share
+        this.createdDate = source.createdDate; // LocalDate: immutable, safe to share
+        this.version     = source.version;
+    }
+
+    @Override
+    public DocumentMetadata copy() {
+        return new DocumentMetadata(this); // delegates to copy constructor
+    }
+
+    public String getAuthor()        { return author; }
+    public LocalDate getCreatedDate(){ return createdDate; }
+    public String getVersion()       { return version; }
+    public void setVersion(String v) { this.version = v; }
+    public void setAuthor(String a)  { this.author = a; }
+
+    @Override public String toString() {
+        return String.format("Metadata{author='%s', date=%s, version='%s'}",
+            author, createdDate, version);
+    }
+}

01-creational/prototype/DocumentRegistry.java

@@ -0,0 +1,21 @@
+package prototype;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class DocumentRegistry {
+
+    private final Map<String, Document> prototypes = new HashMap<>();
+
+    // Register a prototype under a name
+    public void register(String name, Document prototype) {
+        prototypes.put(name, prototype);
+    }
+
+    // Return a fresh copy of the named prototype
+    public Document get(String name) {
+        Document prototype = prototypes.get(name);
+        if (prototype == null) throw new IllegalArgumentException("No prototype: " + name);
+        return prototype.copy(); // always return a copy, never the prototype itself
+    }
+}

01-creational/prototype/Main.java

@@ -1,33 +1,47 @@
 package prototype;
 
-import java.util.ArrayList;
+import java.time.LocalDate;
 import java.util.List;
 
 public class Main {
+
     public static void main(String[] args) {
-        System.out.println("=== Prototype Pattern Demo ===\n");
 
-        List<Shape> originals = new ArrayList<>();
+        // Create the original document (imagine this was loaded from a database)
-        originals.add(new Circle(10, "red"));
+        DocumentMetadata metadata = new DocumentMetadata("Alice", LocalDate.of(2025, 1, 15), "1.0");
-        originals.add(new Rectangle(20, 30, "blue"));
+        Document original = new Document(
+            "Q1 Report",
+            "Revenue increased by 12%...",
+            List.of("finance", "quarterly"),
+            metadata
+        );
 
-        // Clone each shape - no need to know the concrete type
+        System.out.println("Original: " + original);
-        List<Shape> copies = new ArrayList<>();
-        for (Shape shape : originals) {
-            copies.add(shape.clone());
-        }
 
-        // Mutate copies - originals are unaffected
+        // Clone the document and apply only the differences
-        copies.get(0).setColor("green");
+        Document draft = original.copy();
-        copies.get(0).move(5, 5);
+        draft.setTitle("Q1 Report — DRAFT");
-        copies.get(1).setColor("yellow");
+        draft.addTag("draft");
+        draft.getMetadata().setAuthor("Bob");    // only the copy's metadata changes
+        draft.getMetadata().setVersion("1.0-draft");
 
-        System.out.println("--- Originals ---");
+        System.out.println("Draft:    " + draft);
-        originals.forEach(System.out::println);
+        System.out.println("Original: " + original); // unchanged — deep copy worked
 
-        System.out.println("\n--- Clones (mutated) ---");
+        // Verify independence
-        copies.forEach(System.out::println);
+        System.out.println("\nSame object? " + (original == draft));                          // false
+        System.out.println("Same tags?   " + (original.getTags() == draft.getTags()));         // false
+        System.out.println("Same meta?   " + (original.getMetadata() == draft.getMetadata())); // false
 
-        System.out.println("\nSame instance? " + (originals.get(0) == copies.get(0)));
+        // Registry demo: register a named template once, then hand out independent copies
+        DocumentRegistry registry = new DocumentRegistry();
+        registry.register("q-report-template", new Document(
+            "Quarterly Report Template", "## Executive Summary\n...",
+            List.of("quarterly", "finance"), metadata));
+
+        Document myReport = registry.get("q-report-template"); // a fresh, independent copy
+        myReport.setTitle("Q2 2025 Report");
+        myReport.addTag("q2");
+        System.out.println("\nFrom registry: " + myReport);
     }
 }

01-creational/prototype/Rectangle.java

@@ -1,26 +0,0 @@
-package prototype;
-
-public class Rectangle extends Shape {
-    private int width;
-    private int height;
-
-    public Rectangle(int width, int height, String color) {
-        this.width  = width;
-        this.height = height;
-        this.color  = color;
-    }
-
-    private Rectangle(Rectangle source) {
-        super(source);
-        this.width  = source.width;
-        this.height = source.height;
-    }
-
-    @Override
-    public Rectangle clone() { return new Rectangle(this); }
-
-    @Override
-    public String toString() {
-        return "Rectangle{color=" + color + ", size=" + width + "x" + height + ", pos=(" + x + "," + y + ")}";
-    }
-}

01-creational/prototype/Shape.java

@@ -1,22 +0,0 @@
-package prototype;
-
-/** Prototype - every shape can clone itself */
-public abstract class Shape {
-    protected String color;
-    protected int x;
-    protected int y;
-
-    protected Shape(Shape source) {
-        this.color = source.color;
-        this.x     = source.x;
-        this.y     = source.y;
-    }
-
-    protected Shape() {}
-
-    public abstract Shape clone();
-
-    public void setColor(String color) { this.color = color; }
-    public String getColor()           { return color; }
-    public void move(int x, int y)     { this.x = x; this.y = y; }
-}

01-creational/singleton/AppConfig.java

@@ -0,0 +1,19 @@
+package singleton;
+public class AppConfig {
+
+    private AppConfig() {
+        System.out.println("Reading configuration from file...");
+    }
+
+    private static class Holder {
+        static final AppConfig INSTANCE = new AppConfig();
+    }
+
+    public static AppConfig getInstance() {
+        return Holder.INSTANCE;
+    }
+
+    public String getProperty(String key) {
+        return System.getProperty(key, "(not set)");
+    }
+}

01-creational/singleton/DatabaseConnection.java

@@ -1,34 +0,0 @@
-package singleton;
-
-/**
- * Thread-safe Singleton using double-checked locking.
- */
-public class DatabaseConnection {
-    private static volatile DatabaseConnection instance;
-    private final String url;
-    private int queryCount = 0;
-
-    private DatabaseConnection() {
-        this.url = "jdbc:mysql://localhost:3306/myapp";
-        System.out.println("Establishing connection to " + url);
-    }
-
-    public static DatabaseConnection getInstance() {
-        if (instance == null) {
-            synchronized (DatabaseConnection.class) {
-                if (instance == null) {
-                    instance = new DatabaseConnection();
-                }
-            }
-        }
-        return instance;
-    }
-
-    public String executeQuery(String sql) {
-        queryCount++;
-        return "Result #" + queryCount + " for: " + sql;
-    }
-
-    public int getQueryCount() { return queryCount; }
-    public String getUrl()     { return url; }
-}

01-creational/singleton/Main.java

@@ -1,19 +1,9 @@
 package singleton;
-
 public class Main {
     public static void main(String[] args) {
-        System.out.println("=== Singleton Pattern Demo ===\n");
+        AppConfig config1 = AppConfig.getInstance();
-
+        AppConfig config2 = AppConfig.getInstance();
-        DatabaseConnection c1 = DatabaseConnection.getInstance();
+        System.out.println("Same instance? " + (config1 == config2)); // true
-        DatabaseConnection c2 = DatabaseConnection.getInstance();
+        System.out.println("db.url = " + config1.getProperty("db.url"));
-        DatabaseConnection c3 = DatabaseConnection.getInstance();
-
-        System.out.println("\nAll three references same instance? " + (c1 == c2 && c2 == c3));
-
-        System.out.println(c1.executeQuery("SELECT * FROM users"));
-        System.out.println(c2.executeQuery("SELECT * FROM orders"));
-        System.out.println(c3.executeQuery("SELECT COUNT(*) FROM products"));
-
-        System.out.println("\nTotal queries: " + c1.getQueryCount());
     }
 }

README.md

@@ -1,6 +1,6 @@
 # GoF Design Patterns in Java
 
-Complete runnable Java 17 implementations of all 23 Gang of Four design patterns.
+Complete runnable Java 25 implementations of all 23 Gang of Four design patterns.
 Each pattern has a dedicated article at [ankurm.com](https://ankurm.com/gof-design-patterns-java/)
 with a UML diagram, step-by-step explanation, and console output.
 
@@ -38,7 +38,7 @@ design-patterns/
 
 ## Prerequisites
 
-- Java 17+ (Eclipse Temurin recommended)
+- Java 25+ (Eclipse Temurin recommended)
 - No build tool required — plain `javac` / `java`
 
 ## Run any pattern
@@ -83,6 +83,81 @@ java -cp out\strategy strategy.Main
 | Template Method | Behavioral | https://ankurm.com/template-method-design-pattern-java/ |
 | Visitor | Behavioral | https://ankurm.com/visitor-design-pattern-java/ |
 
+## Post ↔ Code Mapping
+
+Each article is split into multiple runnable parts. This section maps every post section to the exact file(s) in this repository, so you can jump straight from "what I just read" to "the file that implements it." Updated pattern-by-pattern as each article is verified against Java 25.
+
+### Factory Method (`01-creational/factory-method/`)
+
+| Post Section | File(s) |
+|---|---|
+| The Problem: Object Creation Leaks Into Business Logic | `NotificationService.java` (anti-pattern shown for contrast — not called by `Main`) |
+| Part 1 — The Notification Interface | `Notification.java` |
+| Part 2 — The Concrete Notification Classes | `EmailNotification.java`, `SmsNotification.java`, `PushNotification.java` |
+| Part 3 — The NotificationSender Class | `NotificationSender.java` |
+| Part 4 — The Concrete Sender Subclasses | `EmailSender.java`, `SmsSender.java`, `PushSender.java` |
+| Part 5 — Running It: Client Code and Output | `Main.java` |
+| Adding a New Channel (Slack) | `SlackNotification.java`, `SlackSender.java` |
+
+Run it:
+```bash
+javac 01-creational/factory-method/*.java -d out/factory-method
+java -cp out/factory-method factorymethod.Main
+```
+
+### Abstract Factory (`01-creational/abstract-factory/`)
+
+| Post Section | File(s) |
+|---|---|
+| Part 1 — The Abstract Products: Button and TextField | `Button.java`, `TextField.java` |
+| Part 2 — The Concrete Products (Light family) | `LightButton.java`, `LightTextField.java` |
+| Part 2 — The Concrete Products (Dark family) | `DarkButton.java`, `DarkTextField.java` |
+| Part 3 — The Abstract Factory: UIFactory Interface | `UIFactory.java` |
+| Part 4 — The Concrete Factories | `LightThemeFactory.java`, `DarkThemeFactory.java` |
+| Part 5 — The Client: Application | `Application.java`, `Main.java` |
+
+Run it:
+```bash
+javac 01-creational/abstract-factory/*.java -d out/abstract-factory
+java -cp out/abstract-factory abstractfactory.Main
+# or, for the dark theme family:
+java -Dapp.theme=dark -cp out/abstract-factory abstractfactory.Main
+```
+
+### Builder (`01-creational/builder/`)
+
+| Post Section | File(s) |
+|---|---|
+| Part 1 — The Product: HttpRequest (Immutable) | `HttpRequest.java` |
+| Part 2 — The Director: Encapsulating Common Configurations | `HttpClientConfig.java` |
+| Part 3 — Using the Builder: Client Code | `Main.java` |
+
+Note: the Lombok `@Builder` example and the JDK standard-library snippets (`HttpRequest.newBuilder()`, `StringBuilder`, `ProcessBuilder`) are illustrative only — they are not part of this repository's runnable example.
+
+Run it:
+```bash
+javac 01-creational/builder/*.java -d out/builder
+java -cp out/builder builder.Main
+```
+
+### Prototype (`01-creational/prototype/`)
+
+| Post Section | File(s) |
+|---|---|
+| Part 1 — The Prototype Interface: Copyable | `Copyable.java` |
+| Part 2 — The Nested Object: DocumentMetadata | `DocumentMetadata.java` |
+| Part 3 — The Concrete Prototype: Document | `Document.java` |
+| Part 4 — The Prototype Registry: DocumentRegistry | `DocumentRegistry.java` |
+| Part 5 — Using the Prototype: Client Code | `Main.java` |
+
+Note: the `ShallowVsDeepDemo` snippet (shallow vs. deep copy) and the `Cloneable`-based example are illustrative only — they are not part of this repository's runnable example.
+
+Run it:
+```bash
+javac 01-creational/prototype/*.java -d out/prototype
+java -cp out/prototype prototype.Main
+```
+
 ## Reference
 
 - *Design Patterns: Elements of Reusable Object-Oriented Software* — Gamma, Helm, Johnson, Vlissides