Why don't you use enum ?

Transcript

1. Why don’t you use enum ? Masayuki IZUMI - @izumin5210

   potatotips #20

2. Ƅ Rekimoto Lab. at the University of Tokyo (2008-2015: Akashi-NCT)

   Ɠ Enginner at Wantedly, Inc. (2014.9-2015.2: Dmetlabel, Inc.) 2

3. 2 Ruby JavaScript Android Design pry(main) > izumin.skill_ratio

4. Enum

5. Enum as constants public class Status { public static final

   int OK = 0; public static final int ERROR = -1; }

6. public enum Status { OK, ERROR; } public class Status

   { public static final int OK = 0; public static final int ERROR = -1; } Enum as constants

7. Example - Enum as constants public void onSomethingAction(int status) {

   switch (status) { case Status.OK: Log.d(TAG, "status: OK"); break; case Status.ERROR: Log.d(TAG, "status: ERROR"); break; } }

8. Example - Enum as constants public void onSomethingAction(int status) {

   switch (status) { case Status.OK: // => int Log.d(TAG, "status: OK"); break; case Status.ERROR: // => int Log.d(TAG, "status: ERROR"); break; } }

9. Example - Enum as constants public void onSomethingAction(Status status) {

   Log.d(TAG: "status: " + status.name()); }

10. Example - Enum as constants public void onSomethingAction(Status status) {

    Log.d(TAG: "status: " + status.name()); } \ enum /

11. * type safe ! - "int enum pattern" is fragile

    - Add/Remove a new item easliy * Prefixes of names are unnecessary - Because each enum types has its own namespace Enum as constants

12. Enum that has member constants/methods public enum Status { OK("Succeed

    the process!"), ERROR("Error has occurred..."); private final String message; Status(String message) { this.message = message; } private String getMessage() { return message; } }

13. Enum that has member constants/methods public enum Status { OK("Succeed

    the process!"), ERROR("Error has occurred..."); private final String message; Status(String message) { this.message = message; } private String getMessage() { return message; } }

14. Enum that has member constants/methods public enum Status { OK("Succeed

    the process!"), ERROR("Error has occurred..."); private final String message; Status(String message) { this.message = message; } private String getMessage() { return message; } }

15. Example - Enum that has member constants/methods public void onSomethingAction(int

    status) { switch (status) { case Status.OK: Log.d(TAG, "Succeed the process!"); break; case Status.ERROR: Log.d(TAG, "Error has occurred..."); break; } }

16. Example - Enum that has member constants/methods public void onSomethingAction(Status

    status) { Log.d(TAG, status.getMessage()); }

17. Example - Enum that has member constants/methods public void onSomethingAction(Status

    status) { Log.d(TAG, status.getMessage()); } \ enum /

18. Constant-specific method implementations public enum Status { OK("Succeed the process!")

    { @Override void log(String tag) { Log.d(tag, message); } }, ERROR("Error has occurred...") { @Override void log(String tag) { Log.e(tag, message); } }; // ... abstract void log(String tag); }

19. Constant-specific method implementations public enum Status { OK("Succeed the process!")

    { @Override void log(String tag) { Log.d(tag, message); } }, ERROR("Error has occurred...") { @Override void log(String tag) { Log.e(tag, message); } }; // ... abstract void log(String tag); }

20. Constant-specific method implementations public enum Status { OK("Succeed the process!")

    { @Override void log(String tag) { Log.d(tag, message); } }, ERROR("Error has occurred...") { @Override void log(String tag) { Log.e(tag, message); } }; // ... abstract void log(String tag); }

21. Constant-specific method implementations public enum Status { OK("Succeed the process!")

    { @Override void log(String tag) { Log.d(tag, message); } }, ERROR("Error has occurred...") { @Override void log(String tag) { Log.e(tag, message); } }; // ... abstract void log(String tag); }

22. * type safe !! * Implements comparable / serializable *

    They are immutable / singleton Constants / Methods

23. Event handling with enum

24. Example - handling click event public void onClick(View v) {

    swtich(v.getId()) { case R.id.button1: // do something... break; case R.id.button2: // do something... break; // ... } }

25. Example - handling click event

26. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { @Override public void handle(Context context) { /* ...*/ } }, BUTTON2(R.id.button2) { @Override public void handle(Context context) { /* ...*/ } }; // ... abstract public void handle(Context context); }

27. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { @Override public void handle(Context context) { /* ...*/ } }, BUTTON2(R.id.button2) { @Override public void handle(Context context) { /* ...*/ } }; // ... abstract public void handle(Context context); }

28. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { @Override public void handle(Context context) { /* ...*/ } }, BUTTON2(R.id.button2) { @Override public void handle(Context context) { /* ...*/ } }; // ... abstract public void handle(Context context); }

29. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { /* ... */ }, BUTTON2(R.id.button2) { /* ... */ }; // ... public static ClickEventHandler valueOf(int resId) { for (ClickEventHandler handler : values()) { if (handler.getResId() == resId) { return handler; } } throw new IllegalArgumentException(); } }

30. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { /* ... */ }, BUTTON2(R.id.button2) { /* ... */ }; // ... public static ClickEventHandler valueOf(int resId) { for (ClickEventHandler handler : values()) { if (handler.getResId() == resId) { return handler; } } throw new IllegalArgumentException(); } }

31. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { /* ... */ }, BUTTON2(R.id.button2) { /* ... */ }; // ... public static ClickEventHandler valueOf(int resId) { for (ClickEventHandler handler : values()) { if (handler.getResId() == resId) { return handler; } } throw new IllegalArgumentException(); } }

32. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { /* ... */ }, BUTTON2(R.id.button2) { /* ... */ }, UNKNOWN(-1) { @Override public void handle(Context context) {} }; // ... public static ClickEventHandler valueOf(int resId) { for (ClickEventHandler handler : values()) { if (handler.getResId() == resId) { return handler; } } return UNKNOWN; } }

33. Example - handling click event public enum ClickEventHandler { BUTTON1(R.id.button1)

    { /* ... */ }, BUTTON2(R.id.button2) { /* ... */ }, UNKNOWN(-1) { @Override public void handle(Context context) {} }; // NULL Object pattern // ... public static ClickEventHandler valueOf(int resId) { for (ClickEventHandler handler : values()) { if (handler.getResId() == resId) { return handler; } } return UNKNOWN; } }

34. Example - handling click event public void onClick(View v) {

    ClickEventHandler.valueOf(v.getId()).handle(this); }

35. Example - handling click event public void onClick(View v) {

    ClickEventHandler.valueOf(v.getId()).handle(this); }

36. * Delegates event handling from controller - We can avoid

    fat controller !!!! * Improves testability - Because they are referentially transparent (?) * Other usecases - BLE (BluetoothGattCharacteristic), HTTP response, etc. Event handling with enum

37. Why don’t you use enum ?