Title

Decorator Pattern

Decoration means putting things on or around an entity to make it look more appealing or attractive. This design pattern tries to add more functionality to an object at runtime without having to modify the object itself.

Let’s consider Juice Center, where different kinds of Fruit Juices are made available. Price depends on the Kind of Fruit used for the preparation of Juice. Vendor realizes over a period of time that by adding different toppings like Honey or Dry Fruits he could increase the price of the Juice itself.

Written with StackEdit.

interface FruitJuice {
    void prepare();
    int getPrice();
}

class AppleJuice implements FruitJuice {

    @Override
    public void prepare() {
        System.out.println("Prepare Apple Juice");

    }
    @Override
    public int getPrice() {

        return 10;
    }
}

class OrangeJuice implements FruitJuice {
    @Override
    public void prepare() {
        System.out.println("Prepare Orange Juice");
    }
    @Override
    public int getPrice() {
        return 10;
    }
}

Orange Juice and Apple Juice are the two kind of Juice available at the Juice Center.

abstract class JuiceDecorator implements FruitJuice {

    protected FruitJuice juice;

    JuiceDecorator(FruitJuice fruitJuice) {
        this.juice = fruitJuice;
    }

    public void prepare() {
        this.juice.prepare();
        this.decorate();

    }

    public int getPrice() {

        return juice.getPrice() + this.addCost();
    }

    abstract void decorate();

    abstract int addCost();

}

class HoneyDecorator extends JuiceDecorator {

    HoneyDecorator(FruitJuice fruitJuice) {
        super(fruitJuice);
    }

    @Override
    void decorate() {
        System.out.println("Decorate with Honey");

    }

    @Override
    int addCost() {

        return 5;
    }

}

class DryFruitDecorator extends JuiceDecorator {

    DryFruitDecorator(FruitJuice fruitJuice) {
        super(fruitJuice);
    }

    @Override
    void decorate() {
        System.out.println("Decorate with Dry Fruits");

    }

    @Override
    int addCost() {

        return 30;
    }

}

Two Kinds of Decorators are added , each of these decorators extend from the abstract JuiceDecorator class. It implements the methods decorate() and addCost() which adds the appropriate topping and increases the cost according to the toppings added.

public class DecoratorDemo {

    public static void main(String[] args) {
        FruitJuice appleJuice = new AppleJuice();
        appleJuice.prepare();
        System.out.println("Apple Juice Price : " + appleJuice.getPrice());

        FruitJuice orangeJuice = new OrangeJuice();
        orangeJuice.prepare();
        System.out.println("Orange Juice Price : " + orangeJuice.getPrice());

        FruitJuice honeyDecoratedAppleJuice = new HoneyDecorator(appleJuice);
        honeyDecoratedAppleJuice.prepare();
        System.out.println("Apple Juice with Honey Price : "
                + honeyDecoratedAppleJuice.getPrice());

        FruitJuice dryFruitDecoratedOrangeJuice = new DryFruitDecorator(
                orangeJuice);
        dryFruitDecoratedOrangeJuice.prepare();
        System.out.println("Orange Juice with Dry Fruits Price : "
                + dryFruitDecoratedOrangeJuice.getPrice());

    }

}

Output

Prepare Apple Juice
Apple Juice Price : 10
Prepare Orange Juice
Orange Juice Price : 10
Prepare Apple Juice
Decorate with Honey
Apple Juice with Honey Price : 15
Prepare Orange Juice
Decorate with Dry Fruits
Orange Juice with Dry Fruits Price : 40