获取枚举与int值相关联

Previously, I had my LegNo enums defined simply as:

以前，我将LegNo枚举定义为：

NO_LEG, LEG_ONE, LEG_TWO

and by calling return LegNo.values()[i];, I was able to get the value associated with each enum.

并通过调用return LegNo.values（）[i];，我能够获得与每个枚举相关联的值。

But now I've decided I want the LegNo enum NO_LEG to be the int -1 instead of 0 so I decided to use a private constructor to initialise and set its int value

但是现在我已经决定我希望LegNo枚举NO_LEG为int -1而不是0所以我决定使用私有构造函数初始化并设置其int值

NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);

private LegNo(final int leg) { legNo = leg; }

the only thing now is that because I'm doing it this way the values() method will not work for the NO_LEG enum. How do I get the enum associated with the int? Is there any efficient way of doing this other than using a case switch statement or an if-elseif-elseif

现在唯一的事情是，因为我这样做，所以values（）方法不适用于NO_LEG枚举。如何获得与int关联的枚举？除了使用case switch语句或if-elseif-elseif之外，还有其他有效的方法吗？

I can see a lot of SO questions to do with getting the int value from the enum, but I'm after the reverse.

从enum中获取int值我可以看到很多SO问题，但是我正在反过来。

8 个解决方案

#1

119

You'll have to maintain a mapping inside the enum.

你必须在枚举中维护一个映射。

public enum LegNo {
    NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);

    private int legNo;

    private static Map<Integer, LegNo> map = new HashMap<Integer, LegNo>();

    static {
        for (LegNo legEnum : LegNo.values()) {
            map.put(legEnum.legNo, legEnum);
        }
    }

    private LegNo(final int leg) { legNo = leg; }

    public static LegNo valueOf(int legNo) {
        return map.get(legNo);
    }
}

The static block will be invoked only once, so there is practically no performance issue here.

静态块只会被调用一次，因此这里几乎没有性能问题。

EDIT: Renamed the method to valueOf as it is more inline with other Java classes.

编辑：将方法重命名为valueOf，因为它更符合其他Java类。

#2

You could also include a static method in the enum that iterates through all members and returns the correct one.

您还可以在枚举中包含一个静态方法，该方法遍历所有成员并返回正确的成员。

public enum LegNo {
   NO_LEG(-1),
   LEG_ONE(1),
   LEG_TWO(2);

   private int legIndex;

   private LegNo(int legIndex) { this.legIndex = legIndex; }

   public static LegNo getLeg(int legIndex) {
      for (LegNo l : LegNo.values()) {
          if (l.legIndex == legIndex) return l;
      }
      throw new IllegalArgumentException("Leg not found. Amputated?");
   }
}

Now, if you want to get an Enum value by the integer, you just use:

现在，如果您想通过整数获得Enum值，您只需使用：

int myLegIndex = 1; //expected : LEG_ONE
LegNo myLeg = LegNo.getLeg(myLegIndex);

#3

adarshr's answer adapted to Java 8:

adarshr的答案适用于Java 8：

import static java.util.Arrays.stream;
import static java.util.stream.Collectors.toMap;

import java.util.Map;

public enum LegNo {
    NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);

    private final int legNo;

    private final static Map<Integer, LegNo> map =
            stream(LegNo.values()).collect(toMap(leg -> leg.legNo, leg -> leg));

    private LegNo(final int leg) {
        legNo = leg;
    }

    public static LegNo valueOf(int legNo) {
        return map.get(legNo);
    }
}

#4

You can also access Enum value corresponding to given integer value simply by calling values() method on enum LegNo. It returns field of LegNo enums: LegNo.values[0]; //returns LEG_NO LegNo.values[1]; //returns LEG_ONE LegNo.values[2]; //returns LEG_TWO

您还可以通过调用枚举LegNo上的values（）方法来访问与给定整数值对应的Enum值。它返回LegNo枚举的字段：LegNo.values [0]; //返回LEG_NO LegNo.values [1]; //返回LEG_ONE LegNo.values [2]; //返回LEG_TWO

Not precisely the thing he was looking for, but pretty close though and very simple indeed. (Although the subject is dead it might be useful for someone else.)

不是他正在寻找的东西，但非常接近但确实非常简单。（虽然主题已经死了，但对其他人来说可能有用。）

#5

Java 8 way with default value:

Java 8方式的默认值：

public enum LegNo {
    NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);

    private final int legNo;

    LegNo(int legNo) {
        this.legNo = legNo;
    }

    public static LegNo find(int legNo, Supplier<? extends LegNo> byDef) {
        return Arrays.asList(LegNo.values()).stream()
                .filter(e -> e.legNo == legNo).findFirst().orElseGet(byDef);
    }
}

to call:

致电：

LegNo res = LegNo.find(0, () -> LegNo.NO_LEG);

or with Exception:

或者有例外：

LegNo res = LegNo.find(0, () -> {
    throw new RuntimeException("No found");
});

#6

Since your enum only contains 3 elements, the fastest way will be to just use a series of if else, like you suggested.

由于你的枚举只包含3个元素，最快的方法就是使用一系列if else，就像你建议的那样。

edit: the answer that adarshr provided is better suited for general cases, where there are many enum values, but I think it is an overkill for your problem.

编辑：adarshr提供的答案更适合一般情况，其中有许多枚举值，但我认为这对你的问题来说太过分了。

#7

public enum LegNo {
    NO_LEG(-1), LEG_ONE(1), LEG_TWO(2);

    private int legNo;

    private LegNo(int leg) { legNo = leg; }

    public static LegNo valueOf(int legNo) {
        for (LegNo leg : LegNo.values()) {
            if (leg.legNo == legNo) return leg;
        }   
    }
}

assert LegNo.valueOf(2) == LegNo.LEG_TWO
assert LegNo.valueOf(3) == null

#8

-4

public enum body
{
    NO_LEG = 0,         // bit 1
    LEG_ONE = 2,        // bit 2 
    LEG_TWO = 4,        // bit 3 
    NO_ARM = 8,          // bit 4 
    ARM_ONE = 16,  // bit 5 
    ARM_TWO = 32  // bit 6 

}

use it like this (int)body.LEG_ONE ; /// which returns 2

像这样使用它（int）body.LEG_ONE; ///返回2

this is also very fast, and easy readable since it is done on compile time.

这也非常快，并且易于阅读，因为它是在编译时完成的。

#1

119