Software Design and Development
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Questions and Answers

What allows the visitor class to execute the proper method on an object without using conditionals?

  • Single Dispatch
  • Double Dispatch (correct)
  • Method Overriding
  • Method Overloading
  • What is the main advantage of using the Visitor pattern?

  • It makes the code more complex
  • It reduces code duplication
  • It improves the performance of the application
  • It allows adding new behaviors to nodes without changing the code (correct)
  • What do nodes do when they 'accept' a visitor?

  • They refuse the visitor's method
  • They execute the visitor's method
  • They tell the visitor what method to execute (correct)
  • They ignore the visitor's method
  • What is a common interface extracted for all visitors?

    <p>Visitor interface</p> Signup and view all the answers

    Why can't method overloading be used to solve the problem of calling the correct visitor method?

    <p>Because the exact class of the node object is unknown in advance</p> Signup and view all the answers

    What pattern is related to the idea of adding new behaviors to objects without changing their code?

    <p>Decorator pattern</p> Signup and view all the answers

    What is the main difference between the Visitor pattern and the Composite pattern?

    <p>The Visitor pattern is used for behavior, the Composite pattern is used for structure</p> Signup and view all the answers

    What is the main disadvantage of using the Visitor pattern?

    <p>It makes the code more complex</p> Signup and view all the answers

    What is the main concern of the system architect when it comes to altering existing node classes?

    <p>The changes might break the application due to potential bugs.</p> Signup and view all the answers

    What design pattern is suggested as a solution to the problem of adding XML export functionality to the node classes?

    <p>Visitor pattern</p> Signup and view all the answers

    What is the primary job of the node classes in the given system?

    <p>To work with geodata.</p> Signup and view all the answers

    Why was the initial solution of adding an export method to each node class not ideal?

    <p>Because it would require changing the existing node classes.</p> Signup and view all the answers

    What is the main advantage of using polymorphism in the initial solution?

    <p>It decouples the code that calls the export method from concrete classes of nodes.</p> Signup and view all the answers

    What is the relationship between the nodes in the graph?

    <p>The nodes are connected if there's a road between the real objects they represent.</p> Signup and view all the answers

    Which design pattern is most similar to the Visitor pattern in terms of decoupling behavior from classes?

    <p>Bridge pattern</p> Signup and view all the answers

    What is the main difference between the Visitor pattern and the Proxy pattern?

    <p>The Visitor pattern adds new behavior, while the Proxy pattern adds a layer of abstraction.</p> Signup and view all the answers

    Study Notes

    The Problem with Adding XML Export to Node Classes

    • The system architect refused to allow changes to existing node classes because they were already in production and he didn't want to risk breaking them.
    • The proposed solution to add an export method to each node class and use recursion to export the graph into XML format was rejected.
    • The primary job of node classes was to work with geodata, and adding XML export behavior would be unrelated to their main purpose.

    The Visitor Pattern Solution

    • The Visitor pattern suggests placing new behavior into a separate class called visitor, instead of integrating it into existing classes.
    • The visitor class defines a set of methods, each of which can take arguments of different types, allowing for different implementation for various node classes.
    • The visitor pattern addresses the problem of calling methods with different signatures by using a technique called Double Dispatch.

    Double Dispatch

    • Double Dispatch is a technique that helps execute the proper method on an object without cumbersome conditionals.
    • It delegates the choice of method to the objects being passed as an argument, allowing them to pick a proper method on the visitor.
    • Objects "accept" a visitor and tell it what visiting method should be executed.

    Benefits of the Visitor Pattern

    • The change to the node classes is trivial, and it allows for adding further behaviors without altering the code again.
    • Extracting a common interface for all visitors allows all existing nodes to work with any visitor.
    • Introducing a new behavior related to nodes only requires implementing a new visitor class.

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    Description

    A software development scenario where a feature is refused due to concerns about future changes and code organization.

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