Editing Decorator pattern (section)

==== Second example (coffee making scenario) ====
The next Java example illustrates the use of decorators using coffee making scenario.
In this example, the scenario only includes cost and ingredients.
{{Clear}}
<syntaxhighlight lang="java">
// The interface Coffee defines the functionality of Coffee implemented by decorator
public interface Coffee {
    public double getCost(); // Returns the cost of the coffee
    public String getIngredients(); // Returns the ingredients of the coffee
}

// Extension of a simple coffee without any extra ingredients
public class SimpleCoffee implements Coffee {
    @Override
    public double getCost() {
        return 1;
    }

    @Override
    public String getIngredients() {
        return "Coffee";
    }
}
</syntaxhighlight>

The following classes contain the decorators for all {{mono|Coffee}} classes, including the decorator classes themselves.

<syntaxhighlight lang="java">

// Abstract decorator class - note that it implements Coffee interface
public abstract class CoffeeDecorator implements Coffee {
    private final Coffee decoratedCoffee;

    public CoffeeDecorator(Coffee c) {
        this.decoratedCoffee = c;
    }

    @Override
    public double getCost() { // Implementing methods of the interface
        return decoratedCoffee.getCost();
    }

    @Override
    public String getIngredients() {
        return decoratedCoffee.getIngredients();
    }
}

// Decorator WithMilk mixes milk into coffee.
// Note it extends CoffeeDecorator.
class WithMilk extends CoffeeDecorator {
    public WithMilk(Coffee c) {
        super(c);
    }

    @Override
    public double getCost() { // Overriding methods defined in the abstract superclass
        return super.getCost() + 0.5;
    }

    @Override
    public String getIngredients() {
        return super.getIngredients() + ", Milk";
    }
}

// Decorator WithSprinkles mixes sprinkles onto coffee.
// Note it extends CoffeeDecorator.
class WithSprinkles extends CoffeeDecorator {
    public WithSprinkles(Coffee c) {
        super(c);
    }

    @Override
    public double getCost() {
        return super.getCost() + 0.2;
    }

    @Override
    public String getIngredients() {
        return super.getIngredients() + ", Sprinkles";
    }
}
</syntaxhighlight>

Here's a test program that creates a {{mono|Coffee}} instance which is fully decorated (with milk and sprinkles), and calculate cost of coffee and prints its ingredients:

<syntaxhighlight lang="java">
public class Main {
    public static void printInfo(Coffee c) {
        System.out.println("Cost: " + c.getCost() + "; Ingredients: " + c.getIngredients());
    }

    public static void main(String[] args) {
        Coffee c = new SimpleCoffee();
        printInfo(c);

        c = new WithMilk(c);
        printInfo(c);

        c = new WithSprinkles(c);
        printInfo(c);
    }
}
</syntaxhighlight>

The output of this program is given below:
<pre>
Cost: 1.0; Ingredients: Coffee
Cost: 1.5; Ingredients: Coffee, Milk
Cost: 1.7; Ingredients: Coffee, Milk, Sprinkles
</pre>