**데코레이터 패턴**(Decorator pattern)이란 주어진 상황 및 용도에 따라 어떤 객체에 책임을 덧붙이는 패턴으로, 기능 확장이 필요할 때 서브클래싱 대신 쓸 수 있는 유연한 대안이 될 수 있다.

예
-

### 자바

```
// the Window interface
interface Window {
 public void draw(); // draws the Window
 public String getDescription(); // returns a description of the Window
}

// implementation of a simple Window without any scrollbars
class SimpleWindow implements Window {
 public void draw() {
 // draw window
 }

 public String getDescription() {
 return "simple window";
 }
}

```

아래의 클래스들은 모든 `Window` 클래스들의 데코레이터를 포함하고 있다.

```
// abstract decorator class - note that it implements Window
abstract class WindowDecorator implements Window {
 protected Window decoratedWindow; // the Window being decorated

 public WindowDecorator (Window decoratedWindow) {
 this.decoratedWindow = decoratedWindow;
 }
}

// the first concrete decorator which adds vertical scrollbar functionality
class VerticalScrollBarDecorator extends WindowDecorator {
 public VerticalScrollBarDecorator (Window decoratedWindow) {
 super(decoratedWindow);
 }

 public void draw() {
 drawVerticalScrollBar();
 decoratedWindow.draw();
 }

 private void drawVerticalScrollBar() {
 // draw the vertical scrollbar
 }

 public String getDescription() {
 return decoratedWindow.getDescription() + ", including vertical scrollbars";
 }
}

// the second concrete decorator which adds horizontal scrollbar functionality
class HorizontalScrollBarDecorator extends WindowDecorator {
 public HorizontalScrollBarDecorator (Window decoratedWindow) {
 super(decoratedWindow);
 }

 public void draw() {
 drawHorizontalScrollBar();
 decoratedWindow.draw();
 }

 private void drawHorizontalScrollBar() {
 // draw the horizontal scrollbar
 }

 public String getDescription() {
 return decoratedWindow.getDescription() + ", including horizontal scrollbars";
 }
}

```

`Window` 인스턴스를 만드는 테스트 프로그램은 아래와 같다.

```
public class DecoratedWindowTest {
 public static void main(String[] args) {
 // create a decorated Window with horizontal and vertical scrollbars
 Window decoratedWindow = new HorizontalScrollBarDecorator (
 new VerticalScrollBarDecorator(new SimpleWindow()));

 // print the Window's description
 System.out.println(decoratedWindow.getDescription());
 }
}

```

### C++

```
#include <iostream>

using namespace std;

/\* Component (interface) \*/
class Widget {

public:
 virtual void draw() = 0;
 virtual ~Widget() {}
};

/\* ConcreteComponent \*/
class TextField : public Widget {

private:
 int width, height;

public:
 TextField( int w, int h ){
 width = w;
 height = h;
 }

 void draw() {
 cout << "TextField: "<< width << ", "<< height << '\n';
 }
};

/\* Decorator (interface) \*/
class Decorator : public Widget {

private:
 Widget\* wid; // reference to Widget

public:
 Decorator( Widget\* w ) {
 wid = w;
 }

 void draw() {
 wid->draw();
 }

 ~Decorator() {
 delete wid;
 }
};

/\* ConcreteDecoratorA \*/
class BorderDecorator : public Decorator {

public:
 BorderDecorator( Widget\* w ) : Decorator( w ) { }
 void draw() {
 Decorator::draw();
 cout << "BorderDecorator" << '\n';
 }
};

/\* ConcreteDecoratorB \*/
class ScrollDecorator : public Decorator {
public:
 ScrollDecorator( Widget\* w ) : Decorator( w ) { }
 void draw() {
 Decorator::draw();
 cout << "ScrollDecorator" << '\n';
 }
};

int main( void ) {

 Widget\* aWidget = new BorderDecorator(
 new ScrollDecorator(
 new TextField( 80, 24 )));
 aWidget->draw();
 delete aWidget;
}

```