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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());
    }
}








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