主要是因?yàn)镃onstruct類中的newInstance方法的一個(gè)判斷條件
if ((this.clazz.getModifiers() & 16384) != 0) {
throw new IllegalArgumentException("Cannot reflectively create enum objects");
}
如果是枚舉類型，就會(huì)拋出異常，因此只有枚舉才能避免被反射破壞
反射在通過(guò)newInstance創(chuàng)建對(duì)象時(shí)，會(huì)檢查該類是否ENUM修飾，如果是則拋出異常，反射失敗

public T newInstance(Object... initargs) throws InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException {
        if (!this.override) {
            Class<?> caller = Reflection.getCallerClass();
            this.checkAccess(caller, this.clazz, this.clazz, this.modifiers);
        }

        if ((this.clazz.getModifiers() & 16384) != 0) {
            throw new IllegalArgumentException("Cannot reflectively create enum objects");
        } else {
            ConstructorAccessor ca = this.constructorAccessor;
            if (ca == null) {
                ca = this.acquireConstructorAccessor();
            }

            T inst = ca.newInstance(initargs);
            return inst;
        }
    }

單例模式詳解
https://www.cnblogs.com/chiclee/p/9097772.html