2913. Design Pattern - Decorator
Decorator Pattern

Structural Pattern: Decorator Pattern.

1. Decorator Pattern

The Decorator pattern allows a user to add new functionality to an existing object without altering its structure. This pattern creates a decorator class which wraps the original class and provides additional functionality keeping class methods signature intact.

2. Example

2.1 Shapes

public interface Shape { void draw(); } public class Circle implements Shape { @Override public void draw() { System.out.println("Shape: Circle"); } } public class Rectangle implements Shape { @Override public void draw() { System.out.println("Shape: Rectangle"); } }

2.2 Decorators

public abstract class ShapeDecorator implements Shape { protected Shape decoratedShape; public ShapeDecorator(Shape decoratedShape){ this.decoratedShape = decoratedShape; } public void draw(){ decoratedShape.draw(); } } public class RedShapeDecorator extends ShapeDecorator { public RedShapeDecorator(Shape decoratedShape) { super(decoratedShape); } @Override public void draw() { decoratedShape.draw(); setRedBorder(decoratedShape); } private void setRedBorder(Shape decoratedShape){ System.out.println("Border Color: Red"); } }

2.3 Client

public class Client { public void draw() { Shape circle = new Circle(); Shape redCircle = new RedShapeDecorator(new Circle()); Shape redRectangle = new RedShapeDecorator(new Rectangle()); System.out.println("Circle with normal border"); circle.draw(); System.out.println("\nCircle of red border"); redCircle.draw(); System.out.println("\nRectangle of red border"); redRectangle.draw(); } }

Output.

Circle with normal border Shape: Circle Circle of red border Shape: Circle Border Color: Red Rectangle of red border Shape: Rectangle Border Color: Red

3. Source Files

4. References