add Decorator

Author: arminmokri

src/structural/decorator/Banana.java

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+package structural.decorator;
+
+public class Banana extends WaffleDecorator {
+    public Banana(Waffle waffle) {
+        super(waffle);
+    }
+
+    public String getDescription() {
+        return decoratedWaffle.getDescription() + ", Banana";
+    }
+
+    public double getCost() {
+        return decoratedWaffle.getCost() + 1.0;
+    }
+}

src/structural/decorator/Main.java

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+package structural.decorator;
+
+public class Main {
+    public static void main(String[] args) throws InterruptedException {
+
+        // my favorite one
+        Waffle waffle1 = new RegularWaffle();
+        waffle1 = new Banana(waffle1);
+        waffle1 = new Strawberry(waffle1);
+        waffle1 = new PeanutButter(waffle1);
+        System.out.println(waffle1.getDescription());
+        System.out.println("Total: $" + waffle1.getCost());
+        System.out.println();
+        System.out.flush();
+        Thread.sleep(2000);
+
+        Waffle waffle2 = new RegularWaffle();
+        waffle2 = new Banana(waffle2);
+        waffle2 = new MapleSyrup(waffle2);
+        waffle2 = new Nutella(waffle2);
+        System.out.println(waffle2.getDescription());
+        System.out.println("Total: $" + waffle2.getCost());
+        System.out.println();
+        System.out.flush();
+        Thread.sleep(2000);
+    }
+}

src/structural/decorator/MapleSyrup.java

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+package structural.decorator;
+
+public class MapleSyrup extends WaffleDecorator {
+    public MapleSyrup(Waffle waffle) {
+        super(waffle);
+    }
+
+    public String getDescription() {
+        return decoratedWaffle.getDescription() + ", Maple Syrup";
+    }
+
+    public double getCost() {
+        return decoratedWaffle.getCost() + 0.8;
+    }
+}

src/structural/decorator/Nutella.java

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+package structural.decorator;
+
+public class Nutella extends WaffleDecorator {
+    public Nutella(Waffle waffle) {
+        super(waffle);
+    }
+
+    public String getDescription() {
+        return decoratedWaffle.getDescription() + ", Nutella";
+    }
+
+    public double getCost() {
+        return decoratedWaffle.getCost() + 1.5;
+    }
+}

src/structural/decorator/PeanutButter.java

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+package structural.decorator;
+
+public class PeanutButter extends WaffleDecorator {
+    public PeanutButter(Waffle waffle) {
+        super(waffle);
+    }
+
+    public String getDescription() {
+        return decoratedWaffle.getDescription() + ", Peanut Butter";
+    }
+
+    public double getCost() {
+        return decoratedWaffle.getCost() + 1.3;
+    }
+}

src/structural/decorator/README.md

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+[< Back To Design Patterns](../../../)
+
+# Decorator Design Pattern
+### Please support my repo with your star.
+
+## Definition
+The Decorator Design Pattern is a structural pattern that allows behavior to be added to individual objects, either statically or dynamically, without affecting the behavior of other objects from the same class. It provides a flexible alternative to subclassing for extending functionality, by wrapping an object with a series of decorator classes that implement the same interface.
+
+## Example in Real World/Nature Inspired
+1. **Gift Wrapping:** A gift can be wrapped with decorative layers (boxes, ribbons, paper) that enhance its appearance without altering the actual gift inside.
+2. **Clothing Layers:** A person can wear a base outfit and then add layers like jackets, scarves, or hats — each adding functionality like warmth or style without changing the person.
+3. **Tree Decorations:** A Christmas tree is decorated with lights, ornaments, and garlands. Each added decoration enhances the tree’s look, and they can be combined in various ways.
+4. **Makeup or Accessories:** Just as accessories or makeup enhance someone’s appearance or performance for a specific event, decorators enhance an object’s behavior for specific contexts.
+
+## Real Usage/System Design Problems
+1. **Extending UI Elements:** In GUI frameworks, decorators are used to add scrollbars, borders, or drop shadows to UI components without changing the base class.
+2. **Adding Responsibilities in Logging:** A logging system may decorate messages with timestamps, tags, or formatting styles in a composable way.
+3. **Stream I/O Systems:** In Java I/O, classes like BufferedInputStream, DataInputStream, etc., decorate base input streams to add buffering or data-type handling without modifying the original stream.
+
+## Important Points of Implementation
+- **Same Interface:** Both the core object and decorators implement the same interface, allowing decorators to be nested and treated uniformly.
+- **Composition Over Inheritance:** Functionality is extended through object composition rather than deep inheritance chains, promoting more flexible designs.
+- **Order Matters:** The order in which decorators are applied can affect the final behavior, so careful composition is needed.
+- **Transparent Wrapping:** Clients using the final decorated object should not need to know whether it has been wrapped — interaction remains consistent.
+
+[< Back To Design Patterns](../../../)

src/structural/decorator/RegularWaffle.java

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+package structural.decorator;
+
+public class RegularWaffle implements Waffle {
+    public String getDescription() {
+        return "Regular Waffle";
+    }
+
+    public double getCost() {
+        return 3.0;
+    }
+}

src/structural/decorator/Strawberry.java

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+package structural.decorator;
+
+public class Strawberry extends WaffleDecorator {
+    public Strawberry(Waffle waffle) {
+        super(waffle);
+    }
+
+    public String getDescription() {
+        return decoratedWaffle.getDescription() + ", Strawberry";
+    }
+
+    public double getCost() {
+        return decoratedWaffle.getCost() + 1.2;
+    }
+}

src/structural/decorator/Waffle.java

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+package structural.decorator;
+
+public interface Waffle {
+    String getDescription();
+    double getCost();
+}

src/structural/decorator/WaffleDecorator.java

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+package structural.decorator;
+
+public abstract class WaffleDecorator implements Waffle {
+    protected Waffle decoratedWaffle;
+
+    public WaffleDecorator(Waffle waffle) {
+        this.decoratedWaffle = waffle;
+    }
+
+    public String getDescription() {
+        return decoratedWaffle.getDescription();
+    }
+
+    public double getCost() {
+        return decoratedWaffle.getCost();
+    }
+}