Why don't you use enum ?

【第20回】potatotips(iOS/Android開発Tips共有会) 発表資料 http://connpass.com/event/17624/

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 ?