Design Patterns in Java - Decorator Pattern

Decorator (Wrapper)

• Also named Wrapper
• Is a structural pattern
• Add behavior without affect others
• Single Responsibility Principle
• Compose behavior dynamically
• Ex. OutputStream

• Inheritance based

Ex. Create a Sandwich class that will be wrapped by a Decorator to add flavors

• Create the interface for the Component

public interface Sandwich {

    

    public String make();

    

} 

• Create an implementation for the ConcreteComponent that will be decorated

public class SimpleSandwich implements Sandwich{

    @Override

    public String make() {

        return "bread";

    }

    

}

• Create an abstract class for the decorator 

public abstract class Decorator implements Sandwich{

    

    protected Sandwich sw;

    

    public Decorator(Sandwich sw){

        this.sw = sw;

    }

    

    @Override

    public String make(){

        return sw.make();

    }

    

}

• Create a specific decorator

public class CheeseDecorator extends Decorator{

    

    public CheeseDecorator(Sandwich sw) {

        super(sw);

    }

    

    public String addIngridient(){

        return "cheese";

    }

    

    @Override

    public String make(){

        return sw.make() + addIngridient();

    }

    

}

• Create the main method
• We create a SimpleSandwich and took it to decorated with CheeseDecorator

public class Main {

    

    public static void main (String args[]){

        Sandwich sw = new CheeseDecorator(new SimpleSandwich());

        

        System.out.println(sw.make());

    }

}