Introduction to Design Patterns

Overview

• Design patterns are common solutions to recurring problems in software design.
• They provide a template or a "way of thinking" to solve common issues.
• Popularized by the "Gang of Four" book which categorized them into three groups: Creational, Structural, and Behavioral.

Purpose of Design Patterns

• Facilitate the creation of flexible and reusable code.
• Allow code to be open for extension but closed for modification, enhancing maintainability.

Practical Analogy - Cooking Example

• Example of a Chef class with a prepare() method:
  • Initially designed to take specific cooking instructions for steak.
  • Overloading for each steak type (e.g., WellDone, MediumDone, Vegan) can be cumbersome as more types are added.
  • Better design: Use a single method that takes a general SteakCookingInstruction class, allowing inheritance for specific cooking instructions.

Design Patterns Categories

1. Creational Patterns

• Focus on object creation mechanisms.
• Example: Builder Pattern allows flexible object construction, useful when not all attributes are needed at all times.

2. Structural Patterns

• Concerned with the composition of classes and objects.
• Example: Flyweight Pattern helps in reducing memory usage by sharing common data among similar objects.
  • Useful for cases like storing books where many attributes are shared across objects.

3. Behavioral Patterns

• Deal with communication and responsibilities among objects.
• Examples include:
  • Strategy Pattern: Offers a way to define a family of algorithms, encapsulate each one, and make them interchangeable.
  • Memento Pattern: Allows capturing and externalizing an object's internal state so that it can be restored later.

Conclusion

• Design patterns can accelerate the development process by offering tested and proven development models.
• Learning and recognizing patterns takes practice and experience.
• Design patterns aid in creating robust, efficient, and maintainable code structures.