如何初始化基于Java枚举的Singleton？ [英] How to initialize Java enum based Singleton?

问题描述

初始化基于java枚举的单例的正确方法是什么，如果我必须先对其进行初始化，然后才能使用该对象。

我已经开始编写代码了，但我不知道我是否正确地做。你能帮我执行这个单身吗？

  public enum BitCheck {
 
 INSTANCE; 
 
 private static HashMap< String，String> props = null; 
 
 public synchronized void initialize（HashMap< String，String> properties）{
 if（props == null）{
 props = properties; 
} 
} 
 
 public boolean isAenabled（）{
 returnY.equalsIgnoreCase（props.get（A_ENABLED））; 
} 
 
 public boolean isBenabled（）{
 returnY.equalsIgnoreCase（props.get（B_ENABLED））; 
} 
 
} 
  

解决方案

完全可以为枚举创建构造函数：

  public枚举BitCheck {
 
 INSTANCE; 
 
 BitCheck（）{
 props = new HashMap< String，String>（）; 
} 
 
 private final Map< String，String>道具; 
 
 // .. 
 
} 
  

请注意：

• 道具字段可以是final（我们喜欢 final ）


• 道具不必是 static


• 构造函数被自动和热切地称为

注意到最后一点。由于$ {code>枚举 -include是在加载枚举BitCheck 类时被创建的，所以您无法将任何参数传递给构造函数。当然你可以通过 INSTANCE 声明：

  public enum BitCheck {
 
 INSTANCE（new HashMap< String，String>（））; 
 
 BitCheck（最终的Map< String，String>道具）{
 this.props =道具; 
} 
  

但这没有什么区别，对吧？你想实现什么？也许你真的需要懒惰初始化的单身吗？

What is the proper way to initialize java enum based singleton, if I have to initialize it before I can use the object.

I have started writing the code , but I am not sure if I am doing it right. Could you help me to implement this singleton correct for me?

public enum BitCheck {

    INSTANCE;

    private static HashMap<String, String> props = null;

    public synchronized void  initialize(HashMap<String, String> properties) {
        if(props == null) {
            props = properties;
        }
    }

    public boolean isAenabled(){
        return "Y".equalsIgnoreCase(props.get("A_ENABLED"));
    }

    public boolean isBenabled(){
        return "Y".equalsIgnoreCase(props.get("B_ENABLED"));
    }

}

解决方案

It's perfectly possible to create constructor for enum:

public enum BitCheck {

    INSTANCE;

    BitCheck() {
        props = new HashMap<String, String>();
    }

    private final Map<String, String> props;

    //..

}

Note that:

• props field can be final (we like final)
• props doesn't have to be static
• constructor is called automatically and eagerly for you

Pay attention to the last point. Since enum-singletons are created eagerly when the enum BitCheck class is loaded, you have no way to pass any arguments to the constructor. Of course you can through INSTANCE declaration:

public enum BitCheck {

    INSTANCE(new HashMap<String, String>());

    BitCheck(final Map<String, String> props) {
        this.props = props;
    }

but this doesn't make any difference, right? What do you want to achieve? Maybe you actually need lazy-initialized singleton?

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