java 枚举共享静态查找方法
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Enums shared static look-up method
提问by Boosty
I have the following Enum:
我有以下枚举：
public enum MyEnum{
A(10, "First"), //
B(20, "Second"), //
C(35, "Other options");
private Integer code;
private String description;
private MyEnum(Integer code, String description) {
this.code = code;
this.description = description;
}
public Integer getCode() {
return code;
}
public String getDescription() {
return description;
}
public static MyEnum getValueOf(Integer code) {
for (MyEnum e : MyEnum.values()) {
if (e.getCode().equals(code)) {
return e;
}
}
throw new IllegalArgumentException("No enum const " + MyEnum.class.getName() + " for code \'" + code
+ "\'");
}
}
Which works fine. The getValueOf-method exists because when communicating with an external partner, we only get the code (they chose) to map to. I need the description because I need to show a meaningfull phrase in the GUI.
哪个工作正常。本getValueOf-方法的存在是因为与外部合作伙伴沟通时，我们只获取代码（他们选择）映射到。我需要描述，因为我需要在 GUI 中显示一个有意义的短语。
But I now have a number of similar enum classes. All having their own code & description, and they need the same lookup functionality.
I wanted the getValueOf-method to be generic so I don't need to support 30+ different enums for basically the same method.
但是我现在有许多类似的枚举类。都有自己的代码和描述，他们需要相同的查找功能。我希望getValueOf-method 是通用的，所以我不需要为基本相同的方法支持 30 多个不同的枚举。
To solve this I wanted to make an abstract class to define this method and implement some of the common logic but this is impossible because I can't extend Enum.
为了解决这个问题，我想创建一个抽象类来定义此方法并实现一些通用逻辑，但这是不可能的，因为我无法扩展Enum.
Then I tried to make a Utility class with the following method:
然后我尝试使用以下方法创建一个实用程序类：
public static <T extends Enum<T>> T getValueOf(Enum<T> type, Integer code) {...}
But generics with Enums are confusing and I don't understand how to get this working.
但是枚举的泛型令人困惑，我不明白如何让它工作。
Basically what I want to know is: What is a good approach to define a common utility to an enum?
基本上我想知道的是：定义枚举的通用实用程序的好方法是什么？
采纳答案by Péter T?r?k
You need to pass the actual enum class object as a parameter to your method. Then you can get the enum values using Class.getEnumConstants().
您需要将实际的枚举类对象作为参数传递给您的方法。然后您可以使用Class.getEnumConstants().
In order to be able to access getCode()on the instances, you should define it in an interface and make all your enum types implement that interface:
为了能够访问getCode()实例，您应该在一个接口中定义它并使您的所有枚举类型实现该接口：
interface Encodable {
Integer getCode();
}
public static <T extends Enum<T> & Encodable> T getValueOf(Class<T> enumClass, Integer code) {
for (T e : enumClass.getEnumConstants()) {
if (e.getCode().equals(code)) {
return e;
}
}
throw new IllegalArgumentException("No enum const " + enumClass.getName() + " for code \'" + code
+ "\'");
}
...
public enum MyEnum implements Encodable {
...
}
MyEnum e = getValueOf(MyEnum.class, 10);
回答by Michael Schmei?er
This is a bit tricky because the values()method is static. You would actually need reflection, but there is a nice way to hide this using standard library functionality.
这有点棘手，因为该values()方法是静态的。您实际上需要反射，但有一种很好的方法可以使用标准库功能来隐藏它。
First, define an interface with the methods common to all of your enum types:
首先，使用所有枚举类型通用的方法定义一个接口：
public interface Common {
Integer getCode();
String getDescription();
}
Then, make all your enums implement this interface:
然后，让你的所有枚举实现这个接口：
public enum MyEnum implements Common {...}
The static method you want to have then looks like:
您想要的静态方法如下所示：
public static <T extends Enum<T> & Common> T getValueOf( Class<T> type, Integer code ) {
final EnumSet<T> values = EnumSet.allOf( type );
for(T e : values) {
if(e.getCode().equals( code )) {
return e;
}
}
throw new IllegalArgumentException( "No enum const " + type.getName() + " for code \'" + code + "\'" );
}
