Separating use from construction - Before

gistfile1.java

public class BusinessObject {
  /** @deprecated */
  public void actionMethod() {
    actionMethod(Service.getInstance());
  }

  // A SEAM! A SEAM! New clients should use me!!
  public void actionMethod(ServiceDelegate serviceDelegate) {
    // Other things
    serviceDelegate.doService();
    // Other things
}

// Am I a Service? Am I a Delegate? Can you tell? Do you care?
abstract class Service : ServiceDelegate {
  /** @deprecated Haven't all my clients died yet!? */
  public static Service getInstance() {
    return new ProductionService(new ProductionServiceDelegate());
  }
  public abstract void doService();
}

/** @deprecated Depend on ServiceDelegate directly, if you can */
class ProductionService : Service {
  private final ProductionServiceDelegate delegate;

  public ProductionService(ProductionServiceDelegate delegate) {
    this.delegate = delegate;
  }

  public void doService() {
    delegate.doService();
  }
}

// Look how mockable I am! New clients should use me!!
interface ServiceDelegate {
  void doService();
}

class ProductionServiceDelegate() {
  public ProductionServiceDelegate() {
    // copy from old ProductionService
  }

  public void doService() {
    // copy from old ProductionService
  }
}

Step 1: Push the implementation down into a new class. https://gist.github.com/1259077/b4a258f66b7a9e95c04e7e62040e38b85b867d33

Step 2: Introduce a mockable interface. https://gist.github.com/1259077/0780c77b0d435233adb1ac302fffdede3634b3b9

Step 3: Add the appropriate instructions for new clients to use new code and old clients to migrate when possible. Hope people read them. https://gist.github.com/1259077/1a9cda66e9a8b7856e6af3dafd9df1080dd11853

Awesome example. Thanks.