Design Patterns

Each pattern describes a problem which occurs over and over again in our environment, and then describes the core of the solution to that problem, in such a way that you can use this solution a million times over, without ever doing it the same way twice.

– Christopher Alexander, “A Pattern Language: Towns, Buildings, Construction”

A description of communicating objects and classes that are customized to solve a general design problem in a particular context.

– Erich Gamma, Richard Helm, Ralph Johnson, John Vlissides, “Design Patterns: Elements of Reusable Object-Oriented Software”

Design Pattern

A Design Pattern is a general, reusable solution to a commonly occurring problem within a given context in software design. They are designed to help you write code that is easier to understand, maintain, and extend.

Key Aspects of Design Patterns

• Reusable Solutions:

  Design patterns provide a proven solution that can be applied across different scenarios and projects.

• Contextual:

  They are not one-size-fits-all but are applied to specific problems within a certain context, providing flexibility in implementation.

• Best Practices:

  Patterns are developed from the experience of many developers over time, representing best practices for solving particular problems.

Elements of a Design Pattern

A design pattern has four essential elements:

1. Pattern Name – A shorthand that can be used to concisely describe the design problem, its solution, and consequences. It allows designing at a higher level of abstraction.

2. Context/Problem – Specifies when to apply the pattern.

3. Solution – Describes the elements that make up the solution to the defined problem, their relationships, responsibilities, and collaborations. It does not describe a specific design or implementation.

4. Consequences – The advantages and disadvantages of using the pattern.

A pattern provides an abstract description of a design problem and how a general arrangement of elements (classes and objects) solves that problem.

Pros & Cons of Design Patterns

Pros of Design Patterns

1. Reusability:

   Design patterns provide proven solutions to common problems, promoting code reuse and reducing redundancy.

2. Efficiency:

   Using established patterns can speed up development as developers don’t need to solve problems from scratch.

3. Consistency

   Patterns ensure consistency in code structure, making it easier for multiple developers to work on the same codebase.

4. Communication:

   Design patterns provide a common vocabulary for developers, simplifying discussions about software design and architecture.

5. Maintainability:

   Well-defined patterns can make code easier to understand and maintain, as the structure and purpose of the code are clearer.

6. Scalability:

   Patterns can provide scalable solutions that are flexible enough to handle growth and changes in requirements.

Cons of Design Patterns

1. Overhead:

   Implementing patterns can sometimes introduce additional layers of complexity, making the codebase harder to understand for newcomers.

2. Overuse:

   There’s a risk of overusing design patterns, applying them even when simpler solutions would suffice, leading to over-engineering.

3. Learning Curve:

   Understanding and correctly implementing design patterns requires a certain level of expertise and experience, which can be a barrier for novice developers.

4. Misapplication:

   Patterns can be misapplied to problems they weren’t designed to solve, resulting in inefficient or convoluted code.

5. Maintenance Challenges:

   While patterns can enhance maintainability, they can also make code harder to modify if the pattern isn’t well understood or if the requirements change significantly.

6. Performance:

Some patterns can introduce performance overhead due to additional abstraction layers, which might not be suitable for high-performance applications.

Categories of Design Patterns

Design patterns are often categorized into three main types:

Creational Patterns	Structural Patterns	Behavioral Patterns
Factory Method	Adapter	Template Method
Abstract Factory	Decorator	Strategy
Prototype	Composite	State
Bridge	Proxy	Observer
Singleton	Facade	Chain of Responsibility
Builder	Bridge	Command
	Flyweight	Memento
		Mediator
		Visitor
		Interpreter
		Iterator