Java Reflection和Singleton

Question

为什么反射不能通过以下代码打破私有构造函数来破坏单例模式。 InstanctTwo上应该有一个新实例，但没有。

Constructor[] constructors = EagerInitializedSingleton.class.getDeclaredConstructors();
for (Constructor constructor : constructors) {
  //Below code will destroy the singleton pattern
  constructor.setAccessible(true);
  instanceTwo = (EagerInitializedSingleton) constructor.newInstance();
  break;
}

Answer 1

如果EagerInitializedSingleton是枚举，它就不起作用。 （我不评论它是否适用于其他情况）

class Ideone
{
    enum EagerInitializedSingleton { INSTANCE }

    public static void main (String[] args) throws java.lang.Exception
    {
        Constructor[] constructors = EagerInitializedSingleton.class.getDeclaredConstructors();
        for (Constructor constructor : constructors) {
          //Below code will destroy the singleton pattern
          constructor.setAccessible(true);
          System.out.println((EagerInitializedSingleton) constructor.newInstance());
        }
    }
}

Ideone demo

Exception in thread "main" java.lang.IllegalArgumentException: Cannot reflectively create enum objects
    at java.lang.reflect.Constructor.newInstance(Constructor.java:416)
    at Ideone.main(Main.java:19)