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Why don’t you use enum ?
Masayuki IZUMI - @izumin5210
potatotips #20
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Ƅ Rekimoto Lab. at the University of Tokyo
(2008-2015: Akashi-NCT)
Ɠ Enginner at Wantedly, Inc.
(2014.9-2015.2: Dmetlabel, Inc.)
2
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2
Ruby
JavaScript
Android
Design
pry(main) > izumin.skill_ratio
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Enum
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Enum as constants
public class Status {
public static final int OK = 0;
public static final int ERROR = -1;
}
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public enum Status {
OK,
ERROR;
}
public class Status {
public static final int OK = 0;
public static final int ERROR = -1;
}
Enum as constants
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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;
}
}
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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;
}
}
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Example - Enum as constants
public void onSomethingAction(Status status) {
Log.d(TAG: "status: " + status.name());
}
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Example - Enum as constants
public void onSomethingAction(Status status) {
Log.d(TAG: "status: " + status.name());
}
\ enum /
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* 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
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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;
}
}
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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;
}
}
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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;
}
}
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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;
}
}
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Example - Enum that has member constants/methods
public void onSomethingAction(Status status) {
Log.d(TAG, status.getMessage());
}
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Example - Enum that has member constants/methods
public void onSomethingAction(Status status) {
Log.d(TAG, status.getMessage());
}
\ enum /
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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);
}
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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);
}
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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);
}
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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);
}
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* type safe !!
* Implements comparable / serializable
* They are immutable / singleton
Constants / Methods
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Event handling with enum
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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;
// ...
}
}
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Example - handling click event
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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);
}
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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);
}
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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);
}
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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();
}
}
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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();
}
}
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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();
}
}
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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;
}
}
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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;
}
}
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Example - handling click event
public void onClick(View v) {
ClickEventHandler.valueOf(v.getId()).handle(this);
}
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Example - handling click event
public void onClick(View v) {
ClickEventHandler.valueOf(v.getId()).handle(this);
}
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* 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
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Why don’t you use enum ?