design_pattern.pptx design_pattern design_pattern

design_pattern.pptx design_pattern design_pattern

• 1.
  Design Patterns inSoftware Architecture: Singleton Pattern Dr. Najmul Hassan
• 2.
  Pattern Overview ▶ Designpatterns capture the essence of proven solutions. ▶ Patterns offer a reusable design structure to solve specific problems. ▶ They help designers decide if the pattern fits the current work, can be reused, or serve as a guide for creating new patterns.
• 3.
  Pattern Name: SingletonPattern ▶ The Singleton Pattern ensures a single instance of a class. ▶ It controls access to this one instance.
• 4.
  Intent of SingletonPattern ▶ The Singleton Pattern restricts instantiation to only one object. ▶ Ensures consistent access to this one object.
• 5.
  Motivation: Problem inE-commerce ▶ Imagine an e-commerce website where each user has one shopping cart. ▶ All pages (product, checkout) need to access the same cart instance. ▶ Without Singleton, multiple cart instances could be created, confusing users.
• 6.
  Applicability ▶ Use Singletonwhen a class needs to be uniquely accessible. ▶ Applicable for shared resources (like a logging or configuration manager). ▶ In our example, the cart must be accessible across multiple pages but remain a single instance.
• 7.
  Structure of SingletonPattern ▶ A class has: ▶ A private static instance variable. ▶ A static method to access or create the instance. ▶ A private constructor to prevent external instantiation.
• 8.
  Participants ▶ Singleton class(e.g., ‘ShoppingCart‘) ▶ Instance variable to store the single instance. ▶ Method to access the instance ensuring only one cart per user .
• 9.
  Collaborations ▶ Multiple classes(e.g., Product Page, Checkout Page) access the ‘ShoppingCart‘ instance. ▶ They call the Singleton instance using a method like ‘ShoppingCart::getInstance()‘.
• 10.
  Consequences of SingletonPattern ▶ Advantages: Ensures consistency and saves memory. ▶ Trade-offs: Singleton can be difficult to test due to its global state. ▶ Design Forces: Balancing single access with easy accessibility.
• 11.
  Related Patterns ▶ FactoryPattern: Used to manage object creation. ▶ Monostate Pattern: Provides a similar effect by sharing state among multiple instances.
• 12.
  Wrap-Up ▶ Singleton isa pattern that ensuresone instance of a class. ▶ Useful for consistent shared resources. ▶ Practical for things like shopping carts in e-commerce. Questions?