Decorator

The intent of the decorator pattern is to give objects new responsibilities without overusing inheritance and therefore creating a bunch of classes. Instead Components get decorated to further enhance objects.

Structure

With this structure you can do things in the decorator before after calling wrappedObj.operationA().

Example

public abstract class Beverage {
 String description = "Unknown Beverage";
  
 public String getDescription() {
  return description;
 }
 
 public abstract double cost();
}
public abstract class CondimentDecorator extends Beverage {
 public abstract String getDescription();
}
public class Espresso extends Beverage {
  
 public Espresso() {
  description = "Espresso";
 }
  
 public double cost() {
  return 1.99;
 }
}
public class Milk extends CondimentDecorator {
 Beverage beverage;
 
 public Milk(Beverage beverage) {
  this.beverage = beverage;
 }
 
 public String getDescription() {
  return beverage.getDescription() + ", Milk";
 }
 
 public double cost() {
  return .10 + beverage.cost();
 }
}

Composite DAOs and Repositories