Structural Design Patterns

Structural design patterns are used to simplify the design by identifying a simple way to realize relationships between entities. They help to compose interfaces or objects to form larger structures while keeping these structures flexible and efficient. Below are some common structural patterns along with their descriptions:

1. Facade Pattern

• Description: The Facade pattern provides a simplified interface to a complex subsystem or a set of interfaces in a subsystem. It hides the complexities of the system and provides a client with a simple and easy-to-use interface.
• Components:
  • Facade: The class that provides the simple interface to the client.
  • Subsystem Classes: The classes that perform the actual work. The Facade forwards the client’s requests to these classes.
• Advantages: Simplifies the client’s interaction with the complex system, reduces dependencies between clients and subsystems, and can make the subsystem easier to use.
• Disadvantages: Can become a “god object” if it starts incorporating too much logic beyond just forwarding calls.

2. Proxy Pattern

• Description: The Proxy pattern provides a surrogate or placeholder for another object to control access to it. The proxy object has the same interface as the real object and forwards requests to the real object when necessary.
• Types of Proxies:
  • Virtual Proxy: Manages the creation and access to a resource-intensive object.
  • Remote Proxy: Represents an object located in a different address space.
  • Protection Proxy: Controls access to the original object based on access rights.
• Advantages: Adds a level of control over the real object, can optimize performance (e.g., by delaying object creation or controlling access), and can add additional functionalities (e.g., logging, access control).
• Disadvantages: Adds complexity to the system, and can introduce latency if not designed carefully.

3. Adapter Pattern

• Description: The Adapter pattern allows two incompatible interfaces to work together. It acts as a bridge between two objects, converting the interface of a class into another interface that a client expects.
• Components:
  • Target: The interface that the client expects.
  • Adapter: Implements the Target interface and translates the request from the client into a format understood by the Adaptee.
  • Adaptee: The existing class with an incompatible interface that needs to be adapted.
• Advantages: Promotes reusability of existing functionality, allows classes with incompatible interfaces to work together without modifying their source code.
• Disadvantages: Can lead to increased complexity if overused, and might introduce an additional level of indirection.

4. Decorator Pattern

• Description: The Decorator pattern allows behavior to be added to individual objects, either statically or dynamically, without affecting the behavior of other objects from the same class. It involves a set of decorator classes that are used to wrap concrete components.
• Components:
  • Component: The interface or abstract class defining the objects that can have responsibilities added to them dynamically.
  • Concrete Component: The class that is being decorated with additional functionalities.
  • Decorator: An abstract class or interface that implements the Component interface and contains a reference to a Component object.
  • Concrete Decorators: Classes that extend the Decorator class to add new behaviors or responsibilities to the Component.
• Advantages: Provides greater flexibility than static inheritance, allows for the dynamic addition of responsibilities, and promotes the open/closed principle (objects can be extended without modifying their source code).
• Disadvantages: Can lead to a large number of small classes that are hard to manage and debug, and introduces complexity with multiple layers of decoration.

5. Composite Pattern

• Description: The Composite pattern allows you to compose objects into tree structures to represent part-whole hierarchies. This pattern treats individual objects and compositions of objects uniformly.
• Components:
  • Component: An interface for objects in the composition, including operations that can be applied to both individual objects and composites.
  • Leaf: A basic object that does not have any children.
  • Composite: A class that has children and implements the behavior for components that have sub-components.
• Advantages: Makes it easier to work with complex tree structures, provides a uniform interface for clients, and supports recursive composition.
• Disadvantages: Can make the design overly general, and managing the tree structure can become complex.

6. Bridge Pattern

• Description: The Bridge pattern decouples an abstraction from its implementation so that the two can vary independently. It is often used to avoid a permanent binding between an abstraction and its implementation.
• Components:
  • Abstraction: Defines the abstract interface and maintains a reference to an object of type Implementor.
  • Refined Abstraction: Extends the interface defined by Abstraction.
  • Implementor: An interface for implementation classes. This interface doesn’t need to match the Abstraction’s interface, and there can be multiple implementations of this interface.
  • Concrete Implementor: Implements the Implementor interface.
• Advantages: Allows you to change the implementation without affecting the abstraction and vice versa, promotes the principle of open/closed, and reduces the complexity in the inheritance hierarchy.
• Disadvantages: Can add complexity to the design by introducing multiple layers of abstraction.

7. Flyweight Pattern

• Description: The Flyweight pattern is used to minimize memory usage or computational expenses by sharing as much data as possible with similar objects. It is particularly useful when dealing with large numbers of similar objects.
• Components:
  • Flyweight: The shared object that can be used in multiple contexts.
  • Concrete Flyweight: Implements the Flyweight interface and adds storage for intrinsic state.
  • Unshared Concrete Flyweight: Objects that do not share state.
  • Flyweight Factory: Creates and manages flyweight objects, ensuring that they are shared correctly.
• Advantages: Reduces memory consumption and can improve performance in situations where many similar objects are used.
• Disadvantages: Increases the complexity of the code and can make the system harder to understand and maintain.

8. Composite Pattern

• Description: The Composite pattern is used to treat a group of objects in the same way as a single instance of an object. It composes objects into tree structures to represent part-whole hierarchies.
• Components:
  • Component: The base interface or abstract class for all objects in the hierarchy.
  • Leaf: A concrete implementation that represents an end object in the hierarchy with no children.
  • Composite: A class that can have children, allowing it to form a tree structure.
• Advantages: Simplifies client code by allowing clients to treat individual objects and compositions of objects uniformly. It’s also flexible and makes it easier to add new types of components.
• Disadvantages: Can make the design more complex, especially with a large number of objects, and it can be difficult to restrict certain operations to leaf objects only.

9. Flyweight Pattern

• Description: The Flyweight pattern is used to minimize memory usage by sharing as much data as possible with similar objects. It’s useful when dealing with a large number of objects that share common data.
• Components:
  • Flyweight: An interface for flyweight objects that defines the intrinsic state.
  • Concrete Flyweight: Implements the Flyweight interface and adds storage for intrinsic state, which can be shared.
  • Unshared Flyweight: A flyweight object that is not shared.
  • Flyweight Factory: Creates and manages flyweight objects, ensuring proper sharing.
• Advantages: Reduces memory usage and improves performance by sharing data across many objects.
• Disadvantages: Can increase complexity, and managing shared data requires careful handling to avoid unintended side effects.

These structural design patterns provide different approaches to structuring software, each with its own strengths and trade-offs. The choice of pattern depends on the specific requirements of your system and the problems you aim to solve.

References

1. Facade Pattern

• Refactoring Guru – Facade Pattern:
  • Overview of the Facade pattern with examples, UML diagrams, and practical use cases.
  • Link: Refactoring Guru – Facade Pattern
• GeeksforGeeks – Facade Design Pattern:
  • Provides a detailed explanation with code examples in Java.
  • Link: GeeksforGeeks – Facade Design Pattern

2. Proxy Pattern

• Refactoring Guru – Proxy Pattern:
  • Comprehensive guide on the Proxy pattern with clear examples, UML diagrams, and variations like Virtual Proxy, Remote Proxy, etc.
  • Link: Refactoring Guru – Proxy Pattern
• GeeksforGeeks – Proxy Design Pattern:
  • Offers a simple explanation with code examples to illustrate the Proxy pattern.
  • Link: GeeksforGeeks – Proxy Design Pattern

3. Adapter Pattern

• Refactoring Guru – Adapter Pattern:
  • Detailed explanation with examples and UML diagrams, showing how to implement the Adapter pattern in various scenarios.
  • Link: Refactoring Guru – Adapter Pattern
• GeeksforGeeks – Adapter Design Pattern:
  • Covers the Adapter pattern with practical examples and applications.
  • Link: GeeksforGeeks – Adapter Design Pattern

4. Decorator Pattern

• Refactoring Guru – Decorator Pattern:
  • In-depth coverage of the Decorator pattern with diagrams and examples, explaining how to extend the functionality of objects dynamically.
  • Link: Refactoring Guru – Decorator Pattern
• GeeksforGeeks – Decorator Design Pattern:
  • Provides a concise explanation with real-world examples of how the Decorator pattern is used.
  • Link: GeeksforGeeks – Decorator Design Pattern

5. Composite Pattern

• Refactoring Guru – Composite Pattern:
  • Thorough explanation of the Composite pattern with examples and diagrams, focusing on part-whole hierarchies.
  • Link: Refactoring Guru – Composite Pattern
• GeeksforGeeks – Composite Design Pattern:
  • Detailed overview of the Composite pattern with code examples and use cases.
  • Link: GeeksforGeeks – Composite Design Pattern

6. Bridge Pattern

• Refactoring Guru – Bridge Pattern:
  • Offers a detailed explanation of the Bridge pattern, demonstrating how to decouple abstraction from implementation.
  • Link: Refactoring Guru – Bridge Pattern
• GeeksforGeeks – Bridge Design Pattern:
  • Simplifies the understanding of the Bridge pattern with examples and clear explanations.
  • Link: GeeksforGeeks – Bridge Design Pattern

7. Flyweight Pattern

• Refactoring Guru – Flyweight Pattern:
  • Explains how to reduce memory usage by sharing as much data as possible with similar objects.
  • Link: Refactoring Guru – Flyweight Pattern
• GeeksforGeeks – Flyweight Design Pattern:
  • Provides examples and a detailed explanation of the Flyweight pattern.
  • Link: GeeksforGeeks – Flyweight Design Pattern

These resources provide comprehensive, clear, and practical explanations of the structural design patterns, complete with examples, diagrams, and use cases to help you understand and apply them effectively in your software designs.