Singleton Design Pattern

What is the Singleton Design Pattern in Java?

The Singleton Design Pattern ensures that a class has only one instance throughout the entire application and provides a global access point to that instance.

 Key Goals:

• Only one object of the class exists.
• It is accessible from anywhere in the program.
• The instance is created only when needed (lazy loading - optional)

Why used?

• To avoid creating multiple heavy or conflicting objects.
• To maintain shared configuration or global resources.

How is Singleton Used in Java?

Singleton is commonly used for:

• Database connections
• Logging systems
• Configuration managers
• Thread pools
• Caching mechanisms
• File system managers

Usage steps:

• Make constructor private.
• Create a private static instance of the class.
• Provide a public static method to return that instance.

Real-World Example

Example: Logging System (Logger)

In real software, programs need a single logger to record messages.

If multiple logger objects were created:

• logs might conflict,
• files could become corrupted.

So, the Logger class becomes a Singleton — one shared instance writing to the log file.

Other real-world examples:

• Single Control Room in a company
• Single Print Spooler in an OS
• OS Task Manager instance
  

Code Example:

More Info:  https://www.geeksforgeeks.org/system-design/singleton-design-pattern/