singleton

Singleton Pattern

The Singleton Pattern is one of the simplest and most widely used design patterns in software development. It ensures that a class has only one instance and provides a global point of access to that instance.

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📖 What is the Singleton Pattern?

The Singleton Pattern restricts the instantiation of a class to a single object. This is useful when exactly one object is needed to coordinate actions across the system, such as:

• Managing shared resources (e.g., database connections, logging frameworks).
• Controlling access to a global state or configuration.

Key features:

1. Global Access: The single instance is accessible globally.
2. Controlled Instantiation: Prevents external instantiation of the class.

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🤔 Why Use the Singleton Pattern?

1. Consistency: Ensures there is only one instance of a class across the application.
2. Resource Management: Avoids overhead caused by multiple object instantiations (e.g., connection pooling).
3. Ease of Access: Provides a single point of access for certain behaviors or data.

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🔧 Implementation

The implementation of the Singleton Pattern can be found in PrinterSpooler.java. This class ensures only one instance of the printer spooler is created and provides a global point of access to it.

To explore the implementation, refer to:

• PrinterSpooler.java: The Singleton class.
• Main.java: Demonstrates the usage of the Singleton Pattern.

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🛠️ Example Usage

To see the Singleton Pattern in action, refer to the Main.java file. It demonstrates how the PrinterSpooler class is used to manage print jobs across the system.

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🌐 Real-World Examples

• Configuration Management:
  • Applications like web servers often use a Singleton to manage configuration settings.
• Logging Frameworks:
  • Logging tools like Log4j often follow the Singleton Pattern.
• Thread Pools:
  • Managing thread pools in multi-threaded applications.

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📊 UML Diagram

classDiagram
direction LR
    class Singleton {
        - instance: Singleton
        - Singleton()
        + getInstance(): Singleton
    }

    class SingletonClient {
        - instance: Singleton.getInstance()
    }

    SingletonClient --> Singleton : Use
    Singleton --* Singleton

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Note

If the UML above is not rendering correctly, you can view the diagram from the singleton_uml.png file.

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📝 Key Takeaways

• The Singleton Pattern ensures a single instance of a class and provides global access to it.
• Use it for shared resources or data where multiple instances would cause conflicts or inefficiencies.
• Be mindful of threading and overuse.

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