改变语言顺序：单例模式是一种创建型设计模式，它保证一个类只有一个实例，并提供一个全局访问点来访问这个实例。单例模式的目的是限制类的实例化次数，节约系统资源，避免多个实例对同一资源的竞争。使用了单例模式来确保只有一个DNS客户端实例。避免重复

Singleton Pattern is a creational design pattern that ensures a class has only one instance and provides a global access point to this instance. The purpose of the Singleton Pattern is to limit the number of instances of a class, conserve system resources, and avoid competition between multiple instances for the same resource. Using the Singleton Pattern ensures that there is only one DNS client instance, avoiding the creation of duplicate DNS client objects and improving system performance.