Decorator Design Pattern

Definition

Decorator Design Pattern is a Structural Design Pattern that adds additional behavior or responsibilities to an object at runtime.

Intention

1. Adds additional functionality to an object at runtime.
2. Provides flexible alternative to sub classing.
3. Works as a filter by applying criteria.

Components

Component - Interface for objects that can have additional responsibilities at runtime.
Concrete Components - Objects that are wrapped by additional behavior.
Decorator - Type of additional behavior that will wrap around Concrete Components
Concrete Decorators  - Extends the functionality of the component by adding behavior or features.
Client - The user who needs the Concrete Components to be added new responsibilities. 










Component

 public interface Vehicle {

    public void drive();

}

Concrete Components


public class Car implements Vehicle {

    @Override
    public void drive() {
        System.out.println("Drive with fuel");
    }

}



Decorator


public abstract class FuelDecorator implements Vehicle {

    protected Vehicle vehicle;

    public FuelDecorator(Vehicle vehicle) {

        this.vehicle = vehicle;
    }

    @Override
    public abstract void drive();

}



Concrete Decorators 

 public class HybridType extends FuelDecorator {

    @Override
    public void drive() {
      
         vehicle.drive();
         System.out.println("and Battery");
    }

    public HybridType(Vehicle vehicle) {
        super(vehicle);
      
    }

}

Client

public class Client {

    public static void main(String[] args) {

        Vehicle vehicle = new Car();

        vehicle.drive(); // Output: Drive with fuel

        Vehicle hybridCar = new HybridType(vehicle);
        hybridCar.drive(); // Output: Drive with fuel
                                    // and Battery

    }

}