chain-of-responsibility

Chain of Responsibility Pattern

The Chain of Responsibility Pattern is a behavioral design pattern that allows a request to be passed along a chain of handlers. Each handler processes the request or passes it to the next handler in the chain.

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📖 What is the Chain of Responsibility Pattern?

The Chain of Responsibility Pattern allows you to decouple the sender of a request from its receivers by giving multiple objects the opportunity to handle the request. The request travels along the chain until one of the handlers processes it.

Key features:

1. Decoupling: Reduces coupling between the sender and receivers of the request.
2. Flexible Workflow: Handlers can be added, removed, or reordered without affecting other parts of the code.
3. Dynamic Handling: Allows requests to be processed by multiple handlers in sequence.

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🤔 Why Use the Chain of Responsibility Pattern?

1. Dynamic Request Handling: When multiple handlers can handle a request, and the decision is made at runtime.
2. Maintainability: Simplifies code by avoiding hardcoded conditionals.
3. Extensibility: Easily extend the chain by adding new handlers.

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🔧 Implementation

The implementation of the Chain of Responsibility Pattern can be found in:

• Chain.java: Interface defining the chain's responsibilities.
• Numbers.java: Represents the input data.
• AddNumbers.java, SubtractNumbers.java, MultNumbers.java, DivideNumbers.java: Concrete handlers.
• Main.java: Demonstrates the usage of the Chain of Responsibility Pattern.

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🛠️ Example Usage

To see the Chain of Responsibility Pattern in action, refer to the Main.java file. It demonstrates a chain of handlers performing mathematical operations based on the input.

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🌐 Real-World Examples

• Logging Frameworks:
  • Messages are passed through a chain of loggers with different log levels (INFO, DEBUG, ERROR).
• Request Processing Pipelines:
  • HTTP requests processed by a chain of filters in web applications.
• Event Handling:
  • GUI frameworks often use this pattern to pass events like mouse clicks to appropriate handlers.

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📊 UML Diagram

classDiagram
direction TB
    class Client {
    }

    class Handler {
        +handleRequest()
    }

    class ConcreteHandler1 {
        +handleRequest()
    }

    class ConcreteHandler2 {
        +handleRequest()
    }

    Handler <--o Handler : successor
    Client --> Handler : " send command "
    Handler <|-- ConcreteHandler1
    Handler <|-- ConcreteHandler2

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Note

If the UML above is not rendering correctly, you can view the diagram from the chain-of-responsibility_uml.png file.

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📝 Key Takeaways

• The Chain of Responsibility Pattern allows requests to be processed by a chain of handlers.
• It decouples the sender of a request from its receivers, promoting flexibility and extensibility.
• Use it when multiple objects can handle a request, and the handler isn't known in advance.

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