Question 1: What is the Singleton pattern in software design?

问题 1：什么是软件设计中的单例模式？

Answer:
The Singleton pattern is a creational design pattern that ensures a class has only one instance and provides a global point of access to that instance.

[ 翻译 ]：
单例模式是一种创建型设计模式，它确保一个类只有一个实例，并提供一个全局访问该实例的入口。

1. It restricts the instantiation of a class to a single object.

   [ 翻译 ]：
   它限制类的实例化只能有一个对象。

2. The Singleton pattern is commonly used in cases where a single resource, such as a configuration file or a database connection, needs to be shared across the entire application.

   [ 翻译 ]：
   单例模式通常用于在整个应用程序中需要共享单一资源的情况，比如配置文件或数据库连接。

3. This pattern helps in controlling access to shared resources by ensuring that only one instance of the resource exists.

   [ 翻译 ]：
   该模式通过确保资源只有一个实例存在，帮助控制对共享资源的访问。

Question 2: What are the key characteristics of the Singleton pattern?

问题 2：单例模式的关键特征是什么？

Answer:
The Singleton pattern has three key characteristics: restricted instantiation, global access, and lazy initialization.

[ 翻译 ]：
单例模式有三个关键特征：限制实例化、全局访问和延迟初始化。

1. Restricted instantiation: The class is designed to restrict the creation of new instances, ensuring only one instance exists.

   [ 翻译 ]：
   限制实例化：该类被设计为限制新实例的创建，确保只存在一个实例。

2. Global access: The Singleton instance is globally accessible, meaning any part of the program can access it.

   [ 翻译 ]：
   全局访问：单例实例可以被全局访问，意味着程序的任何部分都可以访问它。

3. Lazy initialization: The Singleton instance is often created when it is first needed, delaying the creation until it is actually used.

   [ 翻译 ]：
   延迟初始化：单例实例通常是在第一次需要时创建的，推迟实例化直到它被真正使用。

Question 3: What are the advantages and disadvantages of the Singleton pattern?

问题 3：单例模式的优点和缺点是什么？

Answer:
The Singleton pattern has both advantages and disadvantages.

[ 翻译 ]：
单例模式既有优点也有缺点。

1. Advantages: It ensures controlled access to a single instance, reduces memory usage by avoiding multiple object creation, and provides a global point of access.

   [ 翻译 ]：
   优点：它确保了对单个实例的受控访问，避免多次创建对象从而减少内存使用，并提供了一个全局访问点。

2. Disadvantages: It can make unit testing more difficult because the Singleton object’s state may persist across tests, and it introduces a global state, which may lead to hidden dependencies.

   [ 翻译 ]：
   缺点：它可能使单元测试更加困难，因为单例对象的状态可能会在测试间保持不变，且它引入了全局状态，可能导致隐藏的依赖关系。

3. It can also violate the Single Responsibility Principle, as the class is tasked with both managing its own lifecycle and fulfilling its core functionality.

   [ 翻译 ]：
   它还可能违反单一职责原则，因为类不仅要管理自己的生命周期，还要执行其核心功能。