What is the difference between using Decorator and Adapter patterns in system design?

The Decorator and Adapter patterns solve different design problems:

• Decorator

  • Allows dynamically adding new responsibilities to objects by wrapping them in other decorator objects.
  • Used to extend functionality without modifying the original class.
  • Example: adding logging or caching to an existing object.

• Adapter

  • Enables objects with incompatible interfaces to work together.
  • Wraps one interface into another expected by the client.
  • Used for integrating third-party libraries or legacy code with a new interface.

In summary:

• Decorator extends the behavior of an object.
• Adapter changes the interface of an object.

Example in C#:

// Adapter
interface ITarget { void Request(); }
class Adaptee { public void SpecificRequest() { } }
class Adapter : ITarget {
    private Adaptee adaptee = new Adaptee();
    public void Request() { adaptee.SpecificRequest(); }
}

// Decorator
interface IComponent { void Operation(); }
class ConcreteComponent : IComponent {
    public void Operation() { /* base implementation */ }
}
class Decorator : IComponent {
    protected IComponent component;
    public Decorator(IComponent component) { this.component = component; }
    public virtual void Operation() {
        component.Operation();
        // additional behavior
    }
}