Structural Design Patterns: Composite and Decorator
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Structural Design Patterns: Composite and Decorator

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What is the primary purpose of the composite pattern?

  • To enable the asynchronous processing of objects in a multi-threaded environment.
  • To allow for the representation of part-whole relationships in a uniform manner. (correct)
  • To create new object types independently of existing types.
  • To enhance the performance of individual objects by separating them from their context.

    • In the composite design pattern, which object type does NOT contain other objects?

  • Composite Object
  • Node Object
  • Parent Object
  • Leaf Object (correct)

    • Which of the following best describes a Composite Object?

  • An object that performs generic operations without regard to its content.
  • An object that manages its own lifecycle and behavior.
  • An object that cannot be part of the part-whole hierarchy.
  • An object that holds references to its children and delegates operations to them. (correct)

    • What defines the structure of the composite design pattern?

    <p>There should be an interface declared for all components.</p> Signup and view all the answers

    Which situation is most appropriate for using the composite pattern?

    <p>When a system treats individual objects and compositions uniformly.</p> Signup and view all the answers

    In a file-directory structure, what does a directory represent?

    <p>A composite object that can contain other files or directories.</p> Signup and view all the answers

    What is a key step in implementing the composite design pattern?

    <p>Implementing common methods for all component types.</p> Signup and view all the answers

    Which of the following describes a 'Component' in the composite pattern?

    <p>It declares the interface for objects in the composition.</p> Signup and view all the answers

    What role does the Component class play in the design pattern described?

    <p>It defines a common interface for all objects.</p> Signup and view all the answers

    What is the primary disadvantage of using inheritance extensively in the coffee shop example?

    <p>It can lead to a significant class explosion.</p> Signup and view all the answers

    How does the Decorator differ from the ConcreteComponent in the given pattern?

    <p>The Decorator has a HAS-A relationship with a ConcreteComponent.</p> Signup and view all the answers

    In the coffee shop class design, what problem arises from creating classes for every condiment combined with each type of beverage?

    <p>There will be an overwhelming number of classes to manage.</p> Signup and view all the answers

    Which of the following statements most accurately describes the ConcreteDecorator?

    <p>It implements additional methods and can alter existing behavior.</p> Signup and view all the answers

    What modification is proposed as a better approach instead of creating many condiment classes?

    <p>Implement decorator pattern with boolean flags.</p> Signup and view all the answers

    Which of the following best describes the interaction between the Decorator and the Component?

    <p>The Decorator contains a reference to the Component.</p> Signup and view all the answers

    What is the purpose of the cost() method in the Beverage class?

    <p>To allow subclasses to set their own pricing.</p> Signup and view all the answers

    What is the additional cost added for a Dark Roast coffee?

    <p>20 rupees</p> Signup and view all the answers

    What problem arises with the simple approach when adding new condiments?

    <p>All existing code must be modified.</p> Signup and view all the answers

    How does the Decorator Pattern compute the total cost?

    <p>It starts from the inner component and adds costs outward.</p> Signup and view all the answers

    What is a benefit of using the Decorator Pattern over a simple method for beverages?

    <p>It allows adding new beverages without modifying existing code.</p> Signup and view all the answers

    Which of the following is a drawback of the simple approach in beverage cost calculation?

    <p>It necessitates rewriting existing methods for every change.</p> Signup and view all the answers

    What must a new condiment do in the Decorator Pattern to compute costs correctly?

    <p>Wrap around the beverage component and implement its own cost logic.</p> Signup and view all the answers

    In the context of the discussed beverage system, what does 'wrapping' refer to?

    <p>Encapsulating components and decorators together.</p> Signup and view all the answers

    What is a potential issue with inheriting condiments for new beverages like iced tea?

    <p>The new beverages may not require certain condiments.</p> Signup and view all the answers

    What is the primary function of the Composite design pattern in the context of file systems?

    <p>To facilitate the manipulation of objects through a common interface.</p> Signup and view all the answers

    Which of the following classes represents a composite class in the implementation of the Composite design pattern?

    <p>Directory</p> Signup and view all the answers

    In the provided application code, what method does the Directory class utilize to calculate its total size?

    <p>getSize()</p> Signup and view all the answers

    What is a characteristic of the TextFile class in the Composite design pattern implementation?

    <p>It implements the File interface.</p> Signup and view all the answers

    Which method would you use to add a file to a directory instance?

    <p>addFile()</p> Signup and view all the answers

    What does the getSize() method of the Directory class return?

    <p>The cumulative size of all child files within the directory.</p> Signup and view all the answers

    Which of the following accurately describes the File interface’s getType() method?

    <p>It returns the type of the stored files.</p> Signup and view all the answers

    How is the root directory related to child files in the provided file structure?

    <p>The root directory serves as the parent that contains child files.</p> Signup and view all the answers

    What is the final cost computed for the beverage that consists of DarkRoast, Mocha, and Whip?

    <p>Rs. 130</p> Signup and view all the answers

    Which beverage class cannot be instantiated on its own?

    <p>Mocha</p> Signup and view all the answers

    What is a primary advantage of using the decorator pattern?

    <p>It allows behaviors to be added or removed dynamically.</p> Signup and view all the answers

    Which of the following statements about the decorator pattern is true?

    <p>Decorators allow for combining several behaviors through wrapping.</p> Signup and view all the answers

    What is the consequence of having multiple decorators stacked on an object?

    <p>It complicates the removal of specific decorators.</p> Signup and view all the answers

    When calling the cost method on a beverage wrapped in multiple decorators, what computation takes place?

    <p>Each decorator adds its cost to the cost of the wrapped beverage.</p> Signup and view all the answers

    Which class represents a concrete component in the decorator pattern example provided?

    <p>DarkRoast</p> Signup and view all the answers

    What defines the relationship between a concrete decorator and its base component?

    <p>Concrete decorators require a base component upon instantiation.</p> Signup and view all the answers

    What is the purpose of the Decorator pattern?

    <p>To attach additional responsibilities to an object dynamically</p> Signup and view all the answers

    What does the Concrete Component do in the Decorator pattern?

    <p>It is the object to which new behavior can be added</p> Signup and view all the answers

    Which of the following is NOT a class involved in the Decorator pattern as described?

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

    How does the cost method operate within the classes of the Decorator pattern?

    <p>It is overridden by both concrete components and decorators</p> Signup and view all the answers

    In the implementation of the Decorator pattern, what role does 'Beverage' serve?

    <p>An abstract class that serves as a base for components</p> Signup and view all the answers

    What is the relationship between Concrete Decorator and Component?

    <p>Concrete Decorator has an instance variable referencing a Component</p> Signup and view all the answers

    Which of the following classes would NOT typically override the cost method?

    <p>Beverage</p> Signup and view all the answers

    Which beverages and their costs are mentioned in the content?

    <p>DarkRoast - 20, Mocha - 50, Whip - 60</p> Signup and view all the answers

    Study Notes

    STRUCTURAL DESIGN PATTERNS

    • This presentation discusses structural design patterns, specifically the Composite and Decorator patterns.
    • These patterns are used in software design to arrange objects in tree structures or to add functionality in a flexible manner.

    COMPOSITE PATTERN

    • Also known as Object Tree
    • A structural design pattern that allows composing objects into tree structures.
    • Enables working with these structures as single or individual objects.
    • "Composite" refers to combining or making from different parts.
    • Provides solutions for operating on groups of objects and individual objects in a similar way.

    REAL LIFE EXAMPLES - COMPOSITE

    • File-directory structure is a common real-life example.
    • Nodes in this structure can be directories or files.
    • Objects may be different types, but treated similarly (e.g., checking size of a file or directory).
    • The directory size is the sum of the sizes of all files inside it.
    • Employee hierarchy in an organization is another example.
    • CEO, managers, and employees are all instances of a person.

    COMPOSITE DESIGN PATTERN STRUCTURE

    • The pattern has two types of objects: Composite and Leaf.
    • Composite Object: Contains other objects; has children (e.g., directory, file folder).
    • Leaf Object: A single object; has no children (e.g., file).

    WHERE CAN WE USE COMPOSITE PATTERN?

    • When representing a part-whole relationship in a tree structure.
    • When composite and individual objects are treated uniformly.
    • When a parent-child relationship is needed.

    STEPS TO IMPLEMENT COMPOSITE DESIGN PATTERN

    • Define leaf and composite objects as the same data type.
    • Implement common methods in leaf and composite objects.
    • Leaf nodes perform their own desired behavior.
    • Composite objects write customized functions for each child to call.

    STRUCTURE & PARTICIPANTS

    • Component: Declares interface for objects in composition and implements default behavior.
    • Leaf: Represents leaf objects in composition; has no children; defines primitive object behavior.
    • Composite: Defines behavior for components with children; stores child components; implements child-related operations.
    • Client: Manipulates objects in composition through the Component interface.

    UML DIAGRAM FOR COMPOSITE DESIGN PATTERN IMPLEMENTATION

    • The diagram shows how to implement the pattern with interfaces for "File" and classes for different file types (e.g., "Directory," "TextFile").

    IMPLEMENTING COMPOSITE DESIGN PATTERN IN JAVA

    • Develops an example for file directory structure with root, subdirectories and files.
    • Shows example Java code for a file interface and classes for TextFile and Directory with implemented methods for type and size.

    APPLICATION CLASS (JAVA CODE)

    • Shows how to create and interact with composite objects in Java.
    • Includes the use of getSize() methods on composite and leaf objects.

    PROS AND CONS - COMPOSITE

    • Pros: Data representation as a tree structure, uniform operations, reduced overhead, and open/closed principle support.
    • Cons: Objects should be compatible, complexity can be increased.

    DECORATOR PATTERN

    • A structural design pattern that adds new behaviors to objects by placing the objects inside special wrapper objects.
    • The decorator uses composition, not inheritance, to extend the behavior of an object at runtime.
    • Also known as wrapper pattern.

    WHERE TO USE THE DECORATOR PATTERN

    • When objects are extended dynamically without altering the original code.
    • When extending behavior is not straightforward using inheritance, due to existing final classes.

    UML CLASS DIAGRAM & PARTICIPANTS (DECORATOR)

    • Component: Defines the interface for objects to have responsibilities added dynamically.
    • Decorator: Implements the same interface as the component being decorated; has a HAS-A relationship with the decorated object.
    • ConcreteComponent: The object that will be dynamically enhanced.
    • ConcreteDecorator: Decorators that enhance the component (add new methods).

    COFFEE SHOP EXAMPLE

    • Shows a situation where using inheritance to add new features (condiments, etc.) results in a huge number of classes.
    • Demonstrates a potential solution using the decorator pattern.

    APPROACHES TO SOLVING THE COFFEE SHOP PROBLEM

    • Approach 1: Uses boolean variables in the Beverage class to indicate condiments, but results in difficulty maintaining code when new condiments are introduced.
    • Approach 2: The decorator approach (using the decorator pattern) is a more maintainable solution.

    DECORATOR PATTERN IMPLEMENTATION

    • Shows code for a Beverage abstract class and subclasses, including examples of concrete classes like DarkRoast and Mocha, with override methods to add cost for condiments and descriptions for printing.

    PROS AND CONS - DECORATOR

    • Pros: Ability to extend object behavior without subclassing, runtime addition/removal of responsibilities, and combined behaviors.
    • Cons: Difficulty in removing specific decorators in a large chain, code maintainability issues with multiple similar decorators.

    QUESTIONS - REVIEW (SUMMARY)

    • Composite: Composing objects into tree structures, enabling use as single units.
    • Decorator: Adding behaviors to objects through wrappers, extending object functionality without subclassing.

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    Description

    Explore the world of structural design patterns with a focus on the Composite and Decorator patterns. This quiz covers their definitions, real-life examples, and applications in software design, specifically how these patterns facilitate the arrangement of objects. Test your understanding of how to effectively use these patterns in different scenarios.

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