Understanding Singleton Class
A Singleton class is a design pattern that restricts the instantiation of a class to one single instance. This is particularly useful when exactly one object is needed to coordinate actions across the system.
Key Characteristics of Singleton Class:
- Single Instance: The primary feature of a Singleton class is that it ensures that only one instance of the class is created throughout the application.
- Global Access: It provides a global point of access to that instance. This means that other parts of the application can easily obtain a reference to the instance without needing to create new objects.
- Controlled Instantiation: The constructor of a Singleton class is typically private or protected, preventing other classes from creating new instances. Instead, a public static method (often called getInstance) is used to retrieve the single instance.
- Lazy Initialization: Singleton classes can be designed to create their instance only when it is needed (lazy initialization), which can improve performance and resource management.
Comparison with Other Class Types:
- Abstract Class: An abstract class can have multiple instances and serves as a blueprint for other classes.
- Virtual Class: The term "virtual class" is not standard in programming terminology but often refers to classes with virtual methods, which also allow multiple instances.
- Friend Class: A friend class allows access to the private and protected members of another class but does not restrict instantiation.
In summary, the Singleton class is unique because it enforces a single instance, making it the correct answer to the question.