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                # Java 枚舉教程 > 原文: [https://beginnersbook.com/2014/09/java-enum-examples/](https://beginnersbook.com/2014/09/java-enum-examples/) 枚舉是一種特殊類型的數據類型,它基本上是常量的集合(集合)。在本教程中,我們將學習如何在 Java 中使用枚舉以及我們可以使用它們的可能場景。 #### 這就是我們定義`Enum`的方式 ```java public enum Directions{ EAST, WEST, NORTH, SOUTH } ``` 這里我們有**枚舉類型**的變量**方向**,它是四個常數`EAST`,`WEST`,`NORTH`和`SOUTH`的集合。 **如何為枚舉類型**賦值? ```java Directions dir = Directions.NORTH; ``` 變量`dir`的類型為`Directions`(即枚舉類型)。此變量可以取可能的四個值(`EAST`,`WEST`,`NORTH`,`SOUTH`)中的任何值。在這種情況下,它設置為`NORTH`。 #### 在`if-else`語句中使用`Enum`類型 這就是我們如何在`if-else`邏輯中使用枚舉變量。 ```java /* You can assign any value here out of * EAST, WEST, NORTH, SOUTH. Just for the * sake of example, I'm assigning to NORTH */ Directions dir = Directions.NORTH; if(dir == Directions.EAST) { // Do something. Write your logic } else if(dir == Directions.WEST) { // Do something else } else if(dir == Directions.NORTH) { // Do something } else { /* Do Something. Write logic for * the remaining constant SOUTH */ } ``` ## 枚舉示例 這只是演示使用枚舉的一個示例。如果您了解核心部分和基礎知識,您就可以根據需求編寫自己的邏輯。 ```java public enum Directions{ EAST, WEST, NORTH, SOUTH } public class EnumDemo { public static void main(String args[]){ Directions dir = Directions.NORTH; if(dir == Directions.EAST) { System.out.println("Direction: East"); } else if(dir == Directions.WEST) { System.out.println("Direction: West"); } else if(dir == Directions.NORTH) { System.out.println("Direction: North"); } else { System.out.println("Direction: South"); } } } ``` **輸出:** ```java Direction: North ``` #### 在`Switch-Case`語句中使用`Enum` 下面是演示在`switch-case`語句中使用枚舉的示例。 ```java public enum Directions{ EAST, WEST, NORTH, SOUTH } public class EnumDemo { Directions dir; public EnumDemo(Directions dir) { this.dir = dir; } public void getMyDirection() { switch (dir) { case EAST: System.out.println("In East Direction"); break; case WEST: System.out.println("In West Direction"); break; case NORTH: System.out.println("In North Direction"); break; default: System.out.println("In South Direction"); break; } } public static void main(String[] args) { EnumDemo obj1 = new EnumDemo(Directions.EAST); obj1.getMyDirection(); EnumDemo obj2 = new EnumDemo(Directions.SOUTH); obj2.getMyDirection(); } } ``` **輸出:** ```java In East Direction In South Direction ``` #### 如何遍歷`Enum`變量 ```java class EnumDemo { public static void main(String[] args) { for (Directions dir : Directions.values()) { System.out.println(dir); } } } ``` 此代碼將顯示所有四個常量。 ## 枚舉字段和方法 讓我們先舉一個例子然后我們將詳細討論它: ```java public enum Directions{ EAST ("E"), WEST ("W"), NORTH ("N"), SOUTH ("S") ; /* Important Note: Must have semicolon at * the end when there is a enum field or method */ private final String shortCode; Directions(String code) { this.shortCode = code; } public String getDirectionCode() { return this.shortCode; } } public class EnumDemo { public static void main(String[] args) { Directions dir = Directions.SOUTH; System.out.println(dir.getDirectionCode()); Directions dir2 = Directions.EAST; System.out.println(dir2.getDirectionCode()); } } ``` 輸出: ```java S E ``` 正如您在本示例中所看到的,我們為每個常量都有一個字段`shortCode`,以及一個方法`getDirectionCode()`,它基本上是該字段的獲取器方法。當我們定義一個像`EAST ("E")`這樣的常量時,它會使用傳遞的參數調用枚舉構造函數(參見上例中的構造函數`Directions`)。這樣,傳遞的值被設置為相應枚舉常數`EAST("E")`的字段的值,它會調用構造函數`Directions("E")`,`this.shortCode = code`,即`this.shortCode = "E"`,常數`EAST`的`shortCode`字段設置為`"E"`。 #### 注意事項: 1)在定義枚舉時,應在任何字段或方法之前首先聲明常量。 2)當在`Enum`中聲明了字段和方法時,枚舉常量列表必須以分號(`;`)結尾。
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