An example showing the Adapter Design pattern, adapted to some account authentication

Adapters.java

/*
 * We want to auth our user on an application.
 * We have two way to auth our user.
 * We can either authenticate the user using his mail and password via Google, thanks to the Google SDK
 * Or we can use the Facebook SDK to auth our user.
 */

public GoogleAuthenticator() {
	public String authenticateViaGoogle(String mail, String password) {
		//Android code
	}
}

public FacebookAuthenticator() {
	public boolean authenticateViaFacebook(String mail, String password) {
		//Facebook code
	}
}


/*
 * Now, we want to be able to either authenticate the user using facebook, or using his mail.
 * We need to create...
 * SOME ADAPTERS !
 */
public interface AuthenticationAdapter() {
	/*
	 * -1 if an error happened; 0 if user is authenticated.
	 */
	int authUser(User u);
}

/*
 * Our implementation of our adapter for a Google authentication
 */
public class GoogleUserAuthenticationAdapter() implements AuthenticationAdapter{
	private GoogleAuthenticator auth;
	public GoogleUserAuthenticationAdapter() {
		this.auth = new GoogleAuthenticator();
	}

	public int authUser(User u) {
		String s = auth.authenticateViaGoogle(u.getEmail(), u.getPassword());
		if(s=="error")
			return -1;
		return 0;
	}
}
/*
 * Our implementation of our adapter for a Facebook authentication
 */
public class FacebookUserAuthenticationAdapter() implements AuthenticationAdapter{
	private FacebookAuthenticator auth;
	public GoogleUserAuthenticationAdapter() {
		this.auth = new FacebookAuthenticator();
	}

	public int authUser(User u) {
		boolean b = auth.authenticateViaFacebook(u.getEmail(), u.getPassword());
		if(b==false)
			return -1;
		return 0;
	}
}


/*
 * Now, we can have our client that work with our adapter...
 * We simply need to get him the right adapter when creating our AuthenticateRequest.
 */
public class AuthenticateRequest {
	private AuthenticationAdapter mAuthAdapter;
	public AuthenticateRequest(AuthenticationAdapter authAdapter) {
		this.mAuthAdapter = authAdapter;
	}
	
	public void authUser(User u) {
		mAuthAdapter.authUser(u);
	}
}