Decorator

☕ Decorator

Decorator is a structural design pattern that lets you attach new behaviors to objects by placing these objects inside special wrapper objects that contain the behaviors.

Applicability

Use Decorator

• to add responsibilities to individual objects dynamically and transparently, that is, without affecting other objects.
• forresponsibilities that canbe withdrawn.
• when extension by subclassing is impractical. Sometimes a large number of independent extensions are possible and would produce an explosion of subclasses to support every combination. Or a class definition maybe hidden or otherwise unavailable for subclassing.

General Structure

• Component : defines the interface for objects that can have responsibilities added to them dynamically.
• ConcreteComponent : defines an object towhich additional responsibilities canbe attached.
• Decorator : maintains a reference to a Component object and defines an interface that conforms to Component's interface.
• ConcreteDecorator : adds responsibilities to the component.

Example

For example we have a car mangement system , suppose we want to buy a basicCar but with more features like (speed regulator , AC , Navigation system ...)

The code source : source folder

  public static void main(String []args){

    Car basicCar = new BasicCar();
    System.out.println("Basic car : "+ basicCar.cost());

    basicCar = new AirConditioner(basicCar);
    System.out.println("Basic Car (with AirConditioner) : "+basicCar.cost());

    basicCar = new SpeedRegulator(basicCar);
    System.out.println("Basic Car (with AC and speed regulator) : "+basicCar.cost());

  }

Output :

    Basic car : 1000.0
    Basic Car (with AirConditioner) : 1400.0
    Basic Car (with AC and speed regulator) : 1600.0