Java 快速導覽 - Enum 型態

Enum 型態為一組固定的常數 (constant) ，用為某些固定的識別名稱，如方向、月份等等，舉例如下

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enum Day {     SUNDAY, MONDAY, TUESDAY, WEDNESDAY,     THURSDAY, FRIDAY, SATURDAY }   class EnumDemo {     Day day;           public EnumDemo(Day day) {         this.day = day;     }           public void monkeydoing() {         switch (day) {             case SUNDAY:                 System.out.println("星期七，猴子刷油漆");                 break;                               case MONDAY:                 System.out.println("星期一，猴子穿新衣");                 break;                               case TUESDAY:                 System.out.println("星期二，猴子肚子餓");                 break;               case WEDNESDAY:                 System.out.println("星期三，猴子去爬山");                 break;                           case THURSDAY:                 System.out.println("星期四，猴子去考試");                 break;                               case FRIDAY:                 System.out.println("星期五，猴子去跳舞");                 break;                               case SATURDAY:                 System.out.println("星期六，猴子去斗六");                 break;         }     }           public static void main(String[] args) {         EnumDemo day1 = new EnumDemo(Day.MONDAY);         day1.monkeydoing();         EnumDemo day2 = new EnumDemo(Day.TUESDAY);         day2.monkeydoing();         EnumDemo day3 = new EnumDemo(Day.WEDNESDAY);         day3.monkeydoing();         EnumDemo day4 = new EnumDemo(Day.THURSDAY);         day4.monkeydoing();         EnumDemo day5 = new EnumDemo(Day.FRIDAY);         day5.monkeydoing();         EnumDemo day6 = new EnumDemo(Day.SATURDAY);         day6.monkeydoing();         EnumDemo day7 = new EnumDemo(Day.SUNDAY);         day7.monkeydoing();     } }   /* 《程式語言教學誌》的範例程式     http://pydoing.blogspot.com/     檔名：EnumDemo.java     功能：示範物件導向的基本觀念     作者：張凱慶     時間：西元 2010 年 10 月 */

編譯後執行，結果如下



第 1 行到第 4 行

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enum Day {     SUNDAY, MONDAY, TUESDAY, WEDNESDAY,     THURSDAY, FRIDAY, SATURDAY }

這表示識別字 Day 為 Enum 型態，有七個值，分別是 SUNDAY 、 MONDAY 、 TUESDAY 、 WEDNESDAY 、 THURSDAY 、 FRIDAY 、 SATURDAY 。


第 7 行

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Day day;

這裡宣告屬性 day 為 Day 型態的變數。因此，函數 main() 的內容

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EnumDemo day1 = new EnumDemo(Day.MONDAY); day1.monkeydoing(); EnumDemo day2 = new EnumDemo(Day.TUESDAY); day2.monkeydoing(); EnumDemo day3 = new EnumDemo(Day.WEDNESDAY); day3.monkeydoing(); EnumDemo day4 = new EnumDemo(Day.THURSDAY); day4.monkeydoing(); EnumDemo day5 = new EnumDemo(Day.FRIDAY); day5.monkeydoing(); EnumDemo day6 = new EnumDemo(Day.SATURDAY); day6.monkeydoing(); EnumDemo day7 = new EnumDemo(Day.SUNDAY); day7.monkeydoing();

day1 的屬性 day 為 Day.MONDAY ， day2 的屬性 day 為 Day.TUESDAY ，餘下類推。然後呼叫方法 monkeydoing() ，程式會依 Day 型態的值印出相對應的字串。

中英文術語對照
常數	constant

參考資料


http://download.oracle.com/javase/tutorial/java/javaOO/enum.html

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