如何獲取枚舉的數值？

Question

假設你有

public enum Week { 
    SUNDAY, MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY 
} 

一個如何得到int表示週日是0，週三是3等？

Answer 1

Week week = Week.SUNDAY; 

int i = week.ordinal(); 

但要小心，如果您在聲明中更改枚舉常量的順序，該值將會改變。解決此獲得的一種方式是一個int值自分配給您的所有枚舉常數是這樣的：

public enum Week 
{ 
    SUNDAY(0), 
    MONDAY(1) 

    private static final Map<Integer,Week> lookup 
      = new HashMap<Integer,Week>(); 

    static { 
      for(Week w : EnumSet.allOf(Week.class)) 
       lookup.put(w.getCode(), w); 
    } 

    private int code; 

    private Week(int code) { 
      this.code = code; 
    } 

    public int getCode() { return code; } 

    public static Week get(int code) { 
      return lookup.get(code); 
    } 
} 

Answer 2

您可以撥打：

MONDAY.ordinal() 

，但我個人的屬性添加到enum存儲該值，將其初始化爲enum構造函數並添加一個函數以獲取該值。這樣更好，因爲如果enum常量被移動，則MONDAY.ordinal的值可能會更改。

Answer 3

Take a look at the API它通常是一個體面的地方開始。雖然我不會猜到沒有遇到過這個問題之前，你打電話給ENUM_NAME.ordinal（）

Answer 4

是的，只需使用序號枚舉對象的方法。

public class Gtry { 
    enum TestA { 
    A1, A2, A3 
    } 

    public static void main(String[] args) { 
    System.out.println(TestA.A2.ordinal()); 
    System.out.println(TestA.A1.ordinal()); 
    System.out.println(TestA.A3.ordinal()); 
    } 

} 

API：

/** 
    * Returns the ordinal of this enumeration constant (its position 
    * in its enum declaration, where the initial constant is assigned 
    * an ordinal of zero). 
    * 
    * Most programmers will have no use for this method. It is 
    * designed for use by sophisticated enum-based data structures, such 
    * as {@link java.util.EnumSet} and {@link java.util.EnumMap}. 
    * 
    * @return the ordinal of this enumeration constant 
    */ 
    public final int ordinal() { 
     return ordinal; 
    }