Working Effectively with Legacy Code (Droidcon SF)

* How are we going to add this new feature when the code is a mess?
* We can’t change this file-- it’s too risky!
* How do I test this class when it depends on X, Y, and Z?
* There is not enough time to make the changes you want!
* What does this code even do!?
* I feel overwhelmed and it’s never going to get any better.

Android isn’t new anymore. Most applications are not greenfield projects. Many of us find ourselves in the position of working on code we didn't author and which we don’t fully understand.

In the spirit of Michael Feathers' classic book, this talk explores ways we can navigate, maintain, improve and evolve Android legacy code. We will cover topics like architecture, refactoring, testing, and dependency breaking techniques using examples from the speakers’ combined 16+ years of experience working on Android.

Transcript

1. Working Effectively with 

   (Android) 

   Legacy Code
   Mohit Sarveiya, Android @ Vimeo
   
   Chuck Greb, Android @ Button
   

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2. Working Effectively with (Android) Legacy Code
   • What is legacy code?
   
   • Seams
   
   • Dependency breaking techniques
   
   • Strategies for changing software
   

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3. Legacy
   Vintage, historic, nostalgia
   

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8. public class ContactActivity extends ListActivity {
   private static boolean isFirstLoad = false;
   @Override public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   ContactApi.instance.initContext(getApplicationContext());
   ContactApi.instance.initContentResolver(getContentResolver());
   ContactApi[] params = new ContactApi[] { ContactApi.instance };
   LoadContactsTask mLoadContactsTask = new LoadContactsTask();
   mLoadContactsTask.execute(params);
   }
   private class LoadContactsTask extends AsyncTask {
   private final ProgressDialog dialog = new ProgressDialog(ContactActivity.this);
   @Override protected void onPreExecute() {
   if (!dialog.isShowing()) {
   if (isFirstLoad) {
   dialog.setMessage("Loading contacts!!...");
   } else {
   dialog.setMessage("Updating contacts!!...");
   }
   dialog.show();
   }
   }
   @Override protected ContactList doInBackground(ContactApi!!... params) {
   return new ContactList(params[0]);
   }
   @Override protected void onPostExecute(final ContactList contacts) {
   if (dialog.isShowing()) {
   dialog.dismiss();
   }
   setListAdapter(new ContactArrayAdapter(ContactActivity.this, R.layout.list_item, contacts));
   }
   }
   private class ContactArrayAdapter extends ArrayAdapter {
   ContactArrayAdapter(Context context, int id, List contacts) {
   super(context, id, contacts);
   }
   @Override public View getView(int position, View convertView, ViewGroup parent) {
   if (convertView !== null) {
   convertView = getLayoutInflater().inflate(R.layout.list_item, null);
   }
   !// !!...
   return convertView;
   }
   }
   }
   

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9. Legacy Code
   What is legacy code? Challenge of legacy code.
   

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10. Problem
    Built many years ago
    
    Large code base
    
    Millions of users
    
    Large tech debt
    

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11. What is Legacy Code?
    Legacy code is untestable code.
    

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12. public class LoginActivity extends BaseAuthActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    final EventCache eventCache = new EventCache();
    LoginManager loginManager = new LoginManager();
    SessionManager sessionManager = SessionManager.getInstance();
    if (!sessionManager.viewOnboardingScreen()) {
    loginManager.login(email, password, new LoginManager.Callback() {
    @Override
    public void onSuccess(User user) {
    Event event = new Event(LOGIN_SUCCESS);
    for (Event cachedEvent : eventCache.getEvents()) {
    if (cachedEvent.getType() !!= event.getType()) {
    event.track();
    eventCache.add(event);
    }
    }
    }
    }

    !//1000 lines of more code…
    }
    

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13. public class LoginActivity extends BaseAuthActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    final EventCache eventCache = new EventCache();
    LoginManager loginManager = new LoginManager();
    SessionManager sessionManager = SessionManager.getInstance();
    if (!sessionManager.viewOnboardingScreen()) {
    loginManager.login(email, password, new LoginManager.Callback() {
    @Override
    public void onSuccess(User user) {
    Event event = new Event(LOGIN_SUCCESS);
    for (Event cachedEvent : eventCache.getEvents()) {
    if (cachedEvent.getType() !!= event.getType()) {
    event.track();
    eventCache.add(event);
    }
    }
    }
    !//1000 lines of more code…
    Singletons
    

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14. public class LoginActivity extends BaseAuthActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    final EventCache eventCache = new EventCache();
    LoginManager loginManager = new LoginManager();
    SessionManager sessionManager = SessionManager.getInstance();
    if (!sessionManager.viewOnboardingScreen()) {
    loginManager.login(email, password, new LoginManager.Callback() {
    @Override
    public void onSuccess(User user) {
    Event event = new Event(LOGIN_SUCCESS);
    for (Event cachedEvent : eventCache.getEvents()) {
    if (cachedEvent.getType() !!= event.getType()) {
    event.track();
    eventCache.add(event);
    }
    }
    }
    !//1000 lines of more code…
    Break Dependencies
    

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15. public class LoginActivity extends BaseAuthActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    final EventCache eventCache = new EventCache();
    LoginManager loginManager = new LoginManager();
    SessionManager sessionManager = SessionManager.getInstance();
    if (!sessionManager.viewOnboardingScreen()) {
    loginManager.login(email, password, new LoginManager.Callback() {
    @Override
    public void onSuccess(User user) {
    Event event = new Event(LOGIN_SUCCESS);
    for (Event cachedEvent : eventCache.getEvents()) {
    if (cachedEvent.getType() !!= event.getType()) {
    event.track();
    eventCache.add(event);
    }
    }
    }
    !//1000 lines of more code…
    Nested Logic
    

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16. public class LoginActivity extends BaseAuthActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_login);
    final EventCache eventCache = new EventCache();
    LoginManager loginManager = new LoginManager();
    SessionManager sessionManager = SessionManager.getInstance();
    if (!sessionManager.viewOnboardingScreen()) {
    loginManager.login(email, password, new LoginManager.Callback() {
    @Override
    public void onSuccess(User user) {
    Event event = new Event(LOGIN_SUCCESS);
    for (Event cachedEvent : eventCache.getEvents()) {
    if (cachedEvent.getType() !!= event.getType()) {
    event.track();
    eventCache.add(event);
    }
    }
    }
    }
    !//1000 lines of more code…

    }
    Deep Inheritance Hierarchies
    LoginActivity
    BaseAuthActivity
    Activity C
    Activity D
    Activity E
    BaseActivity
    

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17. Finding a balance
    Move 

    KPIs
    Incrementally 

    improve
    

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19. Four Reasons for Changing
    Software
    

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20. Four Reasons for Changing Software
    1. Adding a feature
    
    2. Fixing a bug
    
    3. Improving the design
    
    4. Optimizing resource usage
    

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21. Refactoring
    The act of improving design without changing behavior.
    

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22. “
    “
    Any fool can write code that
    computers can understand.
    Good programmers write
    code humans can understand.
    - Martin Fowler
    The old and new Tappan Zee bridge side by side by Andrew Dallos via Flickr Creative Commons
    

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23. Sensing and Separation
    Sensing - break dependencies to sense behavior or values,

    when we can’t access values computed by code.
    
    Separation - break dependencies to separate components,

    when we can’t get code into a test harness.
    

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24. Seam
    A place where you can alter behavior in your program without editing in that place.
    

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25. Seam Types
    • Pre-processing Seams
    
    • Link Seams
    
    • Object Seams
    

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26. Exercise
    Finding the seam
    

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27. public class MainActivity extends Activity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    !// !!...
    NotificationFactory notificationFactory = new NotificationFactory(this);
    notificationFactory.notify("Title", "Body");
    }
    !// !!...
    }
    

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28. public class MainActivity extends Activity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    !// !!...
    NotificationFactory notificationFactory = new NotificationFactory(this);
    notificationFactory.notify("Title", "Body");
    }
    !// !!...
    }
    

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29. public class MainActivity extends Activity implements MainController {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    !// !!...
    MainPresenter presenter = new MainPresenter(this);
    presenter.displayNotification(this);
    }
    !// !!...
    }
    

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30. public class MainPresenter {
    private MainController controller;
    MainPresenter(MainController controller) {
    this.controller = controller;
    }
    void displayNotification(Context context) {
    NotificationFactory notificationFactory = new NotificationFactory(context);
    notificationFactory.notify("Title", "Body");
    }
    !// !!...
    }
    

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31. public class MainActivity extends Activity implements MainController {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    !// !!...
    NotificationFactory notificationFactory = new NotificationFactory(this);
    MainPresenter presenter = new MainPresenter(this, notificationFactory);
    presenter.displayNotification();
    }
    !// !!...
    }
    

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32. public class MainPresenter {
    private MainController controller;
    private NotificationFactory notificationFactory;
    MainPresenter(MainController controller, NotificationFactory notificationFactory) {
    this.controller = controller;
    this.notificationFactory = notificationFactory;
    }
    void displayNotification() {
    notificationFactory.notify("Title", "Body");
    }
    !// !!...
    }
    

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33. Dependency Breaking
    Techniques
    How do I get code under test without changing behavior?
    

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34. Parametrize Constructor
    Dependency Breaking Techniques
    

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35. public class UserProfilePresenter implements BasePresenter {
    public UserProfilePresenter() {
    …
    }
    public void onProfileButtonClick() {
    if (user !== null) {
    DatabaseManager.getInstance().fetchUsers(new Callback() {
    public void onSuccess(User user) {
    view.showProfile(user);
    }
    public void onError() {
    }
    });
    }
    }
    }
    

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36. public class UserProfilePresenter implements BasePresenter {
    public UserProfilePresenter() {
    …
    }
    public void onProfileButtonClick() {
    if (user !== null) {
    DatabaseManager.getInstance().fetchUsers(new Callback() {
    public void onSuccess(User user) {
    view.showProfile(user);
    }
    public void onError() {
    }
    });
    }
    }
    }
    

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37. public class UserProfilePresenter implements BasePresenter {
    public UserProfilePresenter() {
    …
    }
    public void onProfileButtonClick() {
    if (user !== null) {
    DatabaseManager.getInstance().fetchUsers(new Callback() {
    public void onSuccess(User user) {
    view.showProfile(user);
    }
    public void onError() {
    }
    });
    }
    }
    }
    Activity A
    Activity B
    Activity C
    Activity D
    

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38. public class UserProfilePresenter implements BasePresenter {

    

    private DatabaseManager databaseManager;
    public UserProfilePresenter() {
    …
    }
    public UserProfilePresenter(DatabaseManager databaseManager) {
    this.databaseManager = databaseManager;
    }
    …
    }
    

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39. public class UserProfilePresenter implements BasePresenter {

    

    private DatabaseManager databaseManager;
    public UserProfilePresenter() {
    this(DatabaseManager.getInstance());
    }
    public UserProfilePresenter(DatabaseManager databaseManager) {
    this.databaseManager = databaseManager;
    }
    …
    }
    Activity A
    Activity B
    Activity C
    Activity D
    

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40. public class UserProfilePresenter implements BasePresenter {
    private DatabaseManager databaseManager;
    public UserProfilePresenter() {
    this(DatabaseManager.getInstance());
    }
    public UserProfilePresenter(DatabaseManager databaseManager) {
    this.databaseManager = databaseManager;
    }
    public void onProfileButtonClick() {
    if (user !== null) {
    databaseManager.fetchUsers(new Callback() {
    public void onSuccess(User user) {
    view.showProfile(user);
    }
    public void onError() {
    }
    });
    }
    }
    }
    

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41. 1. Identify the constructor to parameterize and make copy. 

    2. Add a parameter to the new constructor. Remove the object
    creation and add assign the parameter to an instance variable. 

    3. Remove the body of the old constructor and replace with a call
    to the new constructor. 

    Parametrize Constructor
    

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42. Introduce Static Setter
    Dependency Breaking Techniques
    

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43. public class UserPresenter {
    private final UserController controller;
    private UserProfile user;
    public UserPresenter(UserController controller) {
    this.controller = controller;
    }
    public void onProfileButtonClick(Context context) {
    if (user !== null) {
    user = DatabaseManager.getInstance().fetchUser(context);
    }
    controller.showProfile(user);
    }
    }
    

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44. public class DatabaseManager {
    private static final DatabaseManager instance = new DatabaseManager();
    public static DatabaseManager getInstance() {
    return instance;
    }
    private DatabaseManager() {
    }
    public UserProfile fetchUser(Context context) {
    UserProfile user = new UserProfile();
    !// Fetch user profile data from SQLite database!!...
    return user;
    }
    }
    

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45. public class DatabaseManager {
    private static DatabaseManager instance = new DatabaseManager();
    public static DatabaseManager getInstance() {
    return instance;
    }
    @VisibleForTesting
    public static void setTestInstance(DatabaseManager instance) {
    DatabaseManager.instance = instance;
    }
    protected DatabaseManager() {
    }
    public UserProfile fetchUser(Context context) {
    UserProfile user = new UserProfile();
    !// Fetch user profile data from SQLite database!!...
    return user;
    }
    }
    

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46. public class DatabaseManager {
    private static DatabaseManager instance = new DatabaseManager();
    public static DatabaseManager getInstance() {
    return instance;
    }
    @VisibleForTesting
    public static void setTestInstance(DatabaseManager instance) {
    DatabaseManager.instance = instance;
    }
    protected DatabaseManager() {
    }
    public UserProfile fetchUser(Context context) {
    UserProfile user = new UserProfile();
    !// Fetch user profile data from SQLite database!!...
    return user;
    }
    }
    

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47. Introduce Static Setter
    1. Decrease the protection on the constructor from private to
    protected so you can subclass and override.
    
    2. Make the static instance mutable be removing keyword final.
    
    3. Add a test-only method to set the instance in the test
    environment.
    

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48. Instance Delegator
    Dependency Breaking Techniques
    

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49. public class VideoDetailsPresenter {
    public void onShowVideoDetails() {
    if (VideoUtils.canComment(video)) {
    view.showCommentBox();
    }
    if (VideoUtils.isDownloadableFile(video)) {
    view.showDownloadButton();
    }
    …
    }
    }
    

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50. public class VideoDetailsPresenter {
    public void onShowVideoDetails() {
    if (VideoUtils.canComment(video)) {
    view.showCommentBox();
    }
    if (VideoUtils.isDownloadableFile(video)) {
    view.showDownloadButton();
    }
    …
    }
    }
    

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51. public class VideoUtils {
    public static Boolean isDRM(Video video) { … }
    public static Boolean isPublic(Video video) { … }
    public static Boolean canComment(Video video) { … }
    public static Boolean shouldMarkAsPrivate(Video video) { … }
    public static Boolean isHlsFile(Video video) { … }
    public static Boolean isDownloadableFile(Video video) { … }
    …
    }
    

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52. public class VideoUtils {
    public VideoUtils() { … }
    public Boolean isCommentingAllowed(Video video) {
    return canComment(video);
    }
    public static Boolean canComment(Video video) { … }
    public Boolean isDownloadable(Video video) {
    return isDownloadableFile(video);
    }
    public static boolean isDownloadableFile(Video video) { … }
    …
    }
    Create public constructor
    

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53. public class VideoUtils {
    public VideoUtils() { … }
    public Boolean isCommentingAllowed(Video video) {
    return canComment(video);
    }
    public static Boolean canComment(Video video) { … }
    public Boolean isDownloadable(Video video) {
    return isDownloadableFile(video);
    }
    public static boolean isDownloadableFile(Video video) { … }
    …
    }
    Create instance delegator
    Create instance delegator
    

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54. public class VideoDetailsPresenter {
    public void onShowVideoDetails(VideoUtils videoUtils) {
    if (videoUtils.isCommentingAllowed(video)) {
    view.showCommentBox();
    }
    if (videoUtils.isDownloadable(video)) {
    view.showDownloadButton();
    }
    …
    }
    …
    }
    

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55. Instance Delegator
    1. Identify a static method that is problematic to use in a test.
    
    2. Create an instance method for the method on the class.
    
    3. Use Parametrize method technique to supply an instance of to
    the location where the static method call was made.
    

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56. Extract Interface
    Dependency Breaking Techniques
    

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57. public class VideoSettingsPresenter {
    private VideoSettingsView view;
    public void updatePrivacySettings() {
    final User user = AuthenticationHelper.getInstance().getCurrentUser();
    if (user.getAccountType() !== AccountType.PRO) {
    view.showUpgradeButtonForHide();
    view.showUpgradeButtonShareLink();
    }
    }
    public void onSaveVideoSettings() {
    final String currentUserId = AuthenticationHelper.getInstance().getCurrentUserId();
    apiClient.saveVideoSettings(userId, videoSettings, callback);
    }
    …
    }
    

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58. public class VideoSettingsPresenter {
    private VideoSettingsView view;
    public void updatePrivacySettings() {
    final User user = AuthenticationHelper.getInstance().getCurrentUser();
    if (user.getAccountType() !== AccountType.PRO) {
    view.showUpgradeButtonForHide();
    view.showUpgradeButtonShareLink();
    }
    }
    public void onSaveVideoSettings() {
    final String currentUserId = AuthenticationHelper.getInstance().getCurrentUserId();
    apiClient.saveVideoSettings(userId, videoSettings, callback);
    }
    …
    }
    

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59. public class AuthenticationHelper {
    private User user;
    public void loginWithEmail(String email, String password) { … }
    public void loginOut() { … }
    public void trackAuthEvent() { … }
    public User getCurrentUser() { … }
    public User getCurrentUserId() { … }
    …
    }
    

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60. public interface UserProvider {
    User getCurrentUser();
    String getCurrentUserId();
    }
    

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61. public class AuthenticationHelper implements UserProvider {
    private User user;
    public void loginWithEmail(String email, String password) { … }
    public void loginOut() { … }
    public void trackAuthEvent() { … }
    @Override
    public User getCurrentUser() { … }
    @Override
    public User getCurrentUserId() { … }
    …
    }
    

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62. public class VideoSettingsPresenter {
    final UserProvider userProvider;
    public VideoSettingsPresenter(final UserProvider userProvider) {
    this.userProvider = userProvider;
    }
    public void updatePrivacySettings() {
    final User user = userProvider.getCurrentUser();
    if (user.getAccountType() !== AccountType.PRO) {
    view.showUpgradeButtonForHide();
    view.showUpgradeButtonShareLink();
    }
    }
    public void onSaveVideoSettings() {
    final String currentUserId = userProvider.getCurrentUserId();
    apiClient.saveVideoSettings(userId, videoSettings, callback);
    } 

    …
    

    

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63. public class VideoSettingsPresenter {
    final UserProvider userProvider;
    public VideoSettingsPresenter(final UserProvider userProvider) {
    this.userProvider = userProvider;
    }
    public void updatePrivacySettings() {
    final User user = userProvider.getCurrentUser();
    if (user.getAccountType() !== AccountType.PRO) {
    view.showUpgradeButtonForHide();
    view.showUpgradeButtonShareLink();
    }
    }
    public void onSaveVideoSettings() {
    final String currentUserId = userProvider.getCurrentUserId();
    apiClient.saveVideoSettings(userId, videoSettings, callback);
    }
    …
    

    

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64. Extract Interface
    1. Create a new interface with the name you’d like to use.
    
    2. Make a class that you are extracting from implement the
    interface.
    
    3. Change the place where you want to use the object so that it
    uses the interface rather than the original class.
    
    4. Compile the system and introduce a new method declaration
    on the interface for each method.
    

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65. Extract Implementor
    Dependency Breaking Techniques
    

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66. public class NotificationFactory {
    private static final int NOTIFICATION_ID = 0x01;
    private Context context;
    public NotificationFactory(Context context) {
    this.context = context;
    }
    public void notify(String title, String body, PendingIntent pendingIntent) {
    !//!!...
    }
    }
    

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67. public interface NotificationFactory {
    void notify(String title, String body, PendingIntent pendingIntent);
    }
    

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68. public class SimpleNotificationFactory implements NotificationFactory {
    private static final int NOTIFICATION_ID = 0x01;
    private Context context;
    public SimpleNotificationFactory(Context context) {
    this.context = context;
    }
    @Override
    public void notify(String title, String body, PendingIntent pendingIntent) {
    !//!!...
    }
    }
    

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69. Extract Implementor
    1. Step 1…
    
    2. Step 2…
    
    3. Step 3…
    

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70. Dependency Breaking Techniques
    • Parameterize Constructor
    
    • Extract Interface
    
    • Instance Delegator
    
    • Introduce Static Setter
    
    • Extract Implementor
    

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71. Strategies for Changing
    Software
    How do I add features to a legacy code base?
    

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72. https://www.pexels.com/photo/shallow-focus-photography-of-brown-tree-trunk-1250260/
    Sprout Method
    Strategies for Changing Software
    

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73. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    for (Event event : events) {
    event.track(); !// HTTP request
    }
    eventCache.getEventList().addAll(events);
    eventCache.save(); !// Write to SharedPrefs
    }
    }
    

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74. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    for (Event event : events) {
    event.track(); !// HTTP request
    }
    eventCache.getEventList().addAll(events);
    eventCache.save(); !// Write to SharedPrefs
    }
    }
    

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75. HTTP
    
    Server
    Shared
    
    Prefs
    

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76. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    for (Event event : events) {
    event.track(); !// HTTP request
    }
    eventCache.getEventList().addAll(events);
    eventCache.save(); !// Write to SharedPrefs
    }
    }
    

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77. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    List eventsToAdd = new ArrayList!<>();
    for (Event event : events) {
    if (!eventCache.getEventList().contains(event)) {
    event.track(); !// HTTP request
    eventsToAdd.add(event);
    }
    }
    eventCache.getEventList().addAll(eventsToAdd);
    eventCache.save(); !// Write to SharedPrefs
    }
    }
    

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78. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    List eventsToAdd = new ArrayList!<>();
    for (Event event : events) {
    if (!eventCache.getEventList().contains(event)) {
    event.track(); !// HTTP request
    eventsToAdd.add(event);
    }
    }
    eventCache.getEventList().addAll(eventsToAdd);
    eventCache.save(); !// Write to SharedPrefs
    }
    }
    

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79. public class EventTracker {
    !// !!...
    List uniqueEvents(List events) {
    ArrayList result = new ArrayList!<>();
    for (Event event : events) {
    if (!eventCache.getEventList().contains(event)) {
    result.add(event);
    }
    }
    return result;
    }
    }
    

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80. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    List eventsToAdd = uniqueEvents(events);
    for (Event event : eventsToAdd) {
    event.track(); !// HTTP request
    }
    eventCache.getEventList().addAll(eventsToAdd);
    eventCache.save(); !// Write to SharedPrefs
    }
    !// !!...
    }
    

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81. public class EventTracker {
    private EventCache eventCache;
    public EventTracker(EventCache eventCache) {
    this.eventCache = eventCache;
    }
    public void trackEvents(List events) {
    List eventsToAdd = uniqueEvents(events);
    for (Event event : eventsToAdd) {
    event.track(); !// HTTP request
    }
    eventCache.getEventList().addAll(eventsToAdd);
    eventCache.save(); !// Write to SharedPrefs
    }
    !// !!...
    }
    

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82. Sprout Method
    1. Identify where you need to make the code change.
    
    2. Write a new method that will do the work required.
    
    3. Pass any local variables needed as argument(s).
    
    4. Write tests for the sprout method.
    
    5. Invoke the sprout method from the original code.
    

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83. https://www.pexels.com/photo/green-leafy-plant-starting-to-grow-on-beige-racks-127713/
    Sprout Class
    Strategies for Changing Software
    

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84. Password
    Email
    Password
    LOG IN
    

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85. public class LoginActivity extends BaseAuthActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    loginButton.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {

    if (!username.getText().toString().isEmpty() !&& !password.getText().toString().isEmpty()) {
    ApiClient apiClient = new ApiClient("https:!//api.example.com/v1/login");
    apiClient.login(username, password, new Callback() {
    @Override
    public void onSuccess() {
    startActivity(new Intent(LoginActivity.this, MainActivity.class));
    }
    @Override
    public void onFailure() {
    Toast.makeText(LoginActivity.this, "Error", LENGTH_SHORT).show();
    }
    });
    }
    }
    });

    !//10000 lines of more code…
    }
    }
    

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86. Password
    Email
    Password
    LOG IN
    Forgot Password?
    

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87. public class LoginPresenter {
    private final ApiClient apiClient;
    public LoginPresenter(final ApiClient apiClient) {
    this.apiClient = apiClient;
    }
    }
    Create a seam for ApiClient
    Sprout a class
    

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88. public class LoginPresenter {
    private final ApiClient apiClient;
    public LoginPresenter(final ApiClient apiClient) {
    this.apiClient = apiClient;
    }
    public void onClickForgotPassword(String username) {
    apiClient.forgotPassword(username, new ApiClient.Callback() {
    @Override
    public void onSuccess() {
    }
    @Override
    public void onError() {
    }
    });
    }
    }
    New feature
    

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89. public class LoginActivity extends AppCompatActivity {
    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    final ApiClient apiClient = new ApiClient("https:!//api.example.com/v1");
    final LoginPresenter loginPresenter = new LoginPresenter(apiClient);
    forgotPasswordButton.setOnClickListener(
    new View.OnClickListener() {
    @Override
    public void onClick(View v) {
    loginPresenter.onClickForgotPassword(usernameTextView);
    }
    });
    }
    !//1000 lines of more code…
    }
    }
    

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90. Sprout Class
    1. Identify dependencies needed for your new logic.
    
    2. Create another class for the new feature. Inject the needed
    dependencies.
    
    3. Update legacy code to use the sprout class.
    

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91. https://www.pexels.com/photo/burrito-chicken-delicious-dinner-461198/
    Wrap Class
    Strategies for Changing Software
    

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92. public class NotificationFactory {
    private static final int NOTIFICATION_ID = 0x01;
    private Context context;
    public NotificationFactory(Context context) {
    this.context = context;
    }
    public void notify(String title, String body, PendingIntent pendingIntent) {
    !//!!...
    }
    }
    

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93. public interface NotificationFactory {
    void notify(String title, String body, PendingIntent pendingIntent);
    }
    

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94. public class SimpleNotificationFactory implements NotificationFactory {
    private static final int NOTIFICATION_ID = 0x01;
    private Context context;
    public SimpleNotificationFactory(Context context) {
    this.context = context;
    }
    @Override
    public void notify(String title, String body, PendingIntent pendingIntent) {
    !//!!...
    }
    }
    

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95. public class TrackingNotificationFactory implements NotificationFactory {
    private NotificationFactory notificationFactory;
    private EventTracker eventTracker;
    public TrackingNotificationFactory(NotificationFactory notificationFactory,
    EventTracker eventTracker) {
    this.notificationFactory = notificationFactory;
    this.eventTracker = eventTracker;
    }
    @Override
    public void notify(String title, String body, PendingIntent pendingIntent) {
    trackEvent();
    notificationFactory.notify(title, body, pendingIntent);
    }
    private void trackEvent() {
    eventTracker.trackEvent(new Event(“notification-shown"));
    }
    }
    

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96. public class TrackingNotificationFactory implements NotificationFactory {
    private NotificationFactory notificationFactory;
    private EventTracker eventTracker;
    public TrackingNotificationFactory(NotificationFactory notificationFactory,
    EventTracker eventTracker) {
    this.notificationFactory = notificationFactory;
    this.eventTracker = eventTracker;
    }
    @Override
    public void notify(String title, String body, PendingIntent pendingIntent) {
    trackEvent();
    notificationFactory.notify(title, body, pendingIntent);
    }
    private void trackEvent() {
    eventTracker.trackEvent(new Event(“notification-shown"));
    }
    }
    

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97. public class TrackingNotificationFactory implements NotificationFactory {
    private NotificationFactory notificationFactory;
    private EventTracker eventTracker;
    public TrackingNotificationFactory(NotificationFactory notificationFactory,
    EventTracker eventTracker) {
    this.notificationFactory = notificationFactory;
    this.eventTracker = eventTracker;
    }
    @Override
    public void notify(String title, String body, PendingIntent pendingIntent) {
    trackEvent();
    notificationFactory.notify(title, body, pendingIntent);
    }
    private void trackEvent() {
    eventTracker.trackEvent(new Event(“notification-shown"));
    }
    }
    

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98. Wrap Class
    1. Identify existing class or method that needs to change.
    
    2. Create a new class that accepts the existing class as a
    constructor argument.
    
    3. Delegate existing method calls to original class.
    
    4. Create a new method on the new class that does the work.
    
    5. Instantiate the wrapper class where the new behavior is
    needed.
    

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99. Strategies for Changing Software
    • Sprout Method
    
    • Sprout Class
    
    • Wrap Class
    

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100. Conclusion
     Where do you go from here?
     

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101. Code Coverage
     20%
     LoC covered
     Filename Covered
     LoginManager.java 10%
     UserProfilePresenter.java 30%
     UserSettingsPresenter.java 40%
     

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102. What problem is important to solve?
     ANRs
     Crashes
     Bugs
     Performance
     KPIs
     Roadmap
     

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103. Thank you!
     Thank you!
     twitter.com/heyitsmohit /ecgreb
     twitter.com
     Mohit Sarveiya Chuck Greb
     /msya
     github.com /ecgreb
     github.com
     

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