Для чего нужен паттерн Decorator

interface Coffee {
    double getCost();
    String getDescription();
}

class SimpleCoffee implements Coffee {
    public double getCost() { return 1.0; }
    public String getDescription() { return "Simple coffee"; }
}

class MilkDecorator implements Coffee {
    private Coffee coffee;
    
    public MilkDecorator(Coffee coffee) {
        this.coffee = coffee;
    }
    
    public double getCost() {
        return coffee.getCost() + 0.5;
    }
    
    public String getDescription() {
        return coffee.getDescription() + ", milk";
    }
}