• It convert the interface of a class into another interface clients expect.
  • Adapter lets classes work together that couldn't otherwise because of incompatible interfaces.
• It can simply wrap the behavior to isolate a class from the underlying implementation.
• The adapter pattern is usually used when there is no control over the target class (adaptee).

Participants

• Adaptee (ComplexSystem)
  • Defines an existing interface that needs adapting.
• Target (IAcceptedContract)
  • Defines the domain-specific interface that client uses.
  • This is an interface which is used by the client to achieve its functionality/request.
• Adapter (ComplexSystemAdapter)
  • Adapts the interface Adaptee to the Target interface.

private static void Main()
{
	IAcceptedContract adapter = new ComplexSystemAdapter();
	foreach (string item in adapter.GetList())
		Console.Write(item);
}

public class ComplexSystem
{
	public string[][] GetComplexItems()
	{
		string[][] employees = new string[4][];

		employees[0] = new string[] { "100", "Deepak", "Team Leader" };
		employees[1] = new string[] { "101", "Rohit", "Developer" };
		employees[2] = new string[] { "102", "Gautam", "Developer" };
		employees[3] = new string[] { "103", "Dev", "Tester" };

		return employees;
	}
}

public interface IAcceptedContract
{
	List<string> GetList();
}    

public class ComplexSystemAdapter : ComplexSystem, IAcceptedContract
{
	public List<string> GetList()
	{
		var employeeList = new List<string>();
		var employees = GetComplexItems();
		foreach (string[] employee in employees)
		{
			employeeList.Add(employee[0]);
			employeeList.Add(employee[1]);
			employeeList.Add(employee[2]);
		}
		return employeeList;
	}
}

• You can achieve loose-coupling between adaptee and adapter by passing the adaptee instance to the constructor:

private static void Main()
{
	var complexSystem = new ComplexSystem();
	IAcceptedContract employeeAdapter = new ComplexSystemAdapter(complexSystem);
	// ...
}

public class ComplexSystemAdapter : IAcceptedContract
{
	private ComplexSystem _ComplexSystem;
	public ComplexSystemAdapter(ComplexSystem complexSystem)
	{
		_ComplexSystem = complexSystem;
	}

	public List<string> GetList()
	{
		// ...
		var employees = _ComplexSystem.GetComplexItems();
		// ...
	}
}

Rules of Thumb

• Adapter makes things work after they're designed.
  • Bridge makes them work before they are.
• Bridge is designed up-front to let the abstraction and the implementation vary independently.
  • Adapter is retrofitted to make unrelated classes work together.
• Adapter provides a different interface to its subject.
  • Proxy provides the same interface.
  • Decorator provides an enhanced interface.
• Adapter is meant to change the interface of an existing object.
  • Decorator enhances another object without changing its interface.
  • Decorator is thus more transparent to the application than an adapter is.
  • As a consequence, Decorator supports recursive composition, which isn't possible with pure Adapters.
• Facade defines a new interface, whereas Adapter reuses an old interface.
  • Remember that Adapter makes two existing interfaces work together as opposed to defining an entirely new one.