Structural Design Patterns: Composite Pattern
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What is the primary role of the Composite class in the context of the Composite Design Pattern?

  • It manages the lifecycle of individual component instances.
  • It defines a common interface for leaves and composites.
  • It stores and defines behavior for components having children. (correct)
  • It solely focuses on manipulating files without child components.

    • What type of files can the Directory class contain?

  • Just directory types.
  • Only image and video files.
  • Any type of files, including other directories. (correct)
  • Only text files.

    • What is the purpose of the Component class in the design pattern described?

  • To define the interface for objects with dynamic responsibilities. (correct)
  • To provide a base for concrete decorators.
  • To implement the concrete operations of the class.
  • To hold the state of the decorators.

    • What type of relationship exists between the Decorator and the ConcreteComponent?

    <p>HAS-A relationship.</p> Signup and view all the answers

    Which method is responsible for adding files to the Directory class?

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

    What issue arises from overusing inheritance in the beverage class design?

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

    What does the getSize() method in the Directory class compute?

    <p>Total size of all child files and directories.</p> Signup and view all the answers

    In the provided implementation, what type does the TextFile class return in its getType() method?

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

    How do ConcreteDecorators enhance the behavior of the component?

    <p>By adding new methods before or after existing methods.</p> Signup and view all the answers

    What method do all subclasses of Beverage override?

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

    In the context of the Composite Design Pattern, what does the term 'leaf' refer to?

    <p>A component that cannot have children.</p> Signup and view all the answers

    Which of the following condiments is NOT listed in the coffee shop example?

    <p>Vanilla syrup</p> Signup and view all the answers

    What is the purpose of the File interface in this design pattern implementation?

    <p>To define methods that both composite and leaf classes must implement.</p> Signup and view all the answers

    How is the size calculated for the Directory object containing child files?

    <p>It aggregates the sizes from each child file.</p> Signup and view all the answers

    In the approach to avoid class explosion, which variable type is added to the Beverage class?

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

    Why is the cost() method not declared as abstract in the modified Beverage class design?

    <p>To enable dynamic addition of condiments during runtime.</p> Signup and view all the answers

    What is the primary purpose of the Composite design pattern?

    <p>To compose objects into tree structures and treat them uniformly</p> Signup and view all the answers

    Which of the following is NOT a characteristic of the Composite pattern?

    <p>Relies on linear rather than hierarchical structures</p> Signup and view all the answers

    In the context of the Composite pattern, what is a Leaf object?

    <p>A single object that does not have children</p> Signup and view all the answers

    What role does the Composite object play in the Composite pattern?

    <p>It manages child elements and defines operations for them</p> Signup and view all the answers

    Which of the following scenarios is most appropriate for applying the Composite pattern?

    <p>When a part-whole relationship exists in a hierarchical structure</p> Signup and view all the answers

    How are Leaf and Composite objects related in the Composite pattern?

    <p>Both are defined as the same data type through inheritance or interface</p> Signup and view all the answers

    When implementing a Composite design pattern, what is a key step to ensure uniform treatment of components?

    <p>Utilize the same interface or extend from a base class for both types</p> Signup and view all the answers

    Which of the following best illustrates the concept of the Composite pattern in real life?

    <p>A hierarchy of employees in a company viewable as a directory</p> Signup and view all the answers

    What does the cost method in the abstract class Beverage signify?

    <p>It allows concrete components to define their own costs.</p> Signup and view all the answers

    What is the role of the Decorator pattern in the context of beverage selection?

    <p>To dynamically extend functionality without subclassing.</p> Signup and view all the answers

    Which class serves as the base class for both concrete components and decorators?

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

    In the given example, which of the following can be considered a concrete component?

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

    What is the typical function of the abstract class CondimentDecorator?

    <p>To define a common interface for condiment-related decorators.</p> Signup and view all the answers

    How do Concrete Decorators differ from Concrete Components?

    <p>They contain instances of components to add behavior.</p> Signup and view all the answers

    What can be inferred about the description variable in the Beverage class?

    <p>It serves as a default descriptor until overridden.</p> Signup and view all the answers

    What would be the immediate consequence of not overriding the cost method in a concrete component?

    <p>The component will always return a default cost of 0.</p> Signup and view all the answers

    What is the primary purpose of the getDescription method in the Beverage class?

    <p>To provide a base description for all beverages</p> Signup and view all the answers

    Which statement accurately describes the relationship between DarkRoast and Beverage?

    <p>DarkRoast is a concrete class that extends Beverage</p> Signup and view all the answers

    What does the Mocha class do when it is constructed with a Beverage?

    <p>It sets the instance variable for decoration purposes</p> Signup and view all the answers

    How does the cost for a beverage decorated with Mocha calculate its total cost?

    <p>It sums the cost of the base beverage with the Mocha cost</p> Signup and view all the answers

    What would b2 = new Mocha(b2) imply in terms of object-oriented principles?

    <p>A beverage is being decorated with additional functionality</p> Signup and view all the answers

    Which class explicitly requires that the methods getDescription and cost be overridden?

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

    What is the output of the following code snippet: Beverage b2 = new DarkRoast(); b2 = new Mocha(b2);?

    <p>Dark roast, Mocha Rs.70</p> Signup and view all the answers

    Why must the cost method be overridden in the concrete classes of decorators?

    <p>To enable calculation of total cost including both beverage and condiment</p> Signup and view all the answers

    What is the final cost of a beverage that is made up of DarkRoast, Mocha, and Whip?

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

    Why can the Mocha class not be instantiated directly without a beverage?

    <p>Mocha requires a constructor argument that is a Beverage.</p> Signup and view all the answers

    What does the decorator pattern allow you to do with an object's behavior?

    <p>You can add or remove responsibilities from an object at runtime.</p> Signup and view all the answers

    What is a disadvantage of using the decorator pattern?

    <p>It can complicate code maintainability due to numerous similar decorators.</p> Signup and view all the answers

    When the cost method is called on the beverage that is a combination of DarkRoast and Mocha, what cost is initially returned from DarkRoast?

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

    In the example given, what is the role of the Whip class in relation to the other beverages?

    <p>It enhances the beverage created by wrapping the existing one.</p> Signup and view all the answers

    How would the classes DarkRoast, Mocha, and Whip relate to each other in terms of class hierarchies?

    <p>DarkRoast is the superclass, while Mocha and Whip are decorators.</p> Signup and view all the answers

    What is necessary before you can instantiate the Mocha class?

    <p>A concrete Beverage must be passed in its constructor.</p> Signup and view all the answers

    Study Notes

    STRUCTURAL DESIGN PATTERNS

    • Structural design patterns compose classes or objects into larger structures, and then define ways to use these structures

    COMPOSITE PATTERN

    • Also known as: Object Tree
    • Composite is a structural design pattern that lets you compose objects into tree structures and then work with these structures as if they were individual objects
    • From the name, "Composite" means the combination or made from different parts
    • This pattern provides a solution to operate on groups of objects and single objects in a similar way
    • Real-life examples include file-directory structures, where a node can be a directory or a file
      • Even though directories and files are different types of objects, they can be treated similarly (e.g., checking the size of a directory, which is the sum of sizes of all files within that directory)
    • Another real-life example is employee hierarchy structure (CEO, managers, employees)
      • All employees, managers and the CEO are instances of a person
    •  Structure of the composite pattern:
        1. Composite Object: An object that contains other objects. This can be a directory (file folder)
        1. Leaf Object: A single object that does not have children (e.g., a file).

    WHERE CAN WE USE COMPOSITE PATTERN?

    • When you want to represent a part-whole relationship in a tree structure (Objects can be represented in a tree structure hierarchy)
    • Composite and individual objects are treated uniformly
    • Need to define parent-child relationships

    STEPS TO IMPLEMENT COMPOSITE DESIGN PATTERN

    • Define leaf and composite objects as the same data type
    • Implement an interface or extend a class
    • Write common methods for all leaf and composite objects
    • Leaf node performs its own desired behavior
    • Composite object writes a customized function or each child of this node can call this function

    STRUCTURE & PARTICIPANTS

    • Component: Declares an interface for objects in the composition, and implements default behaviors common to all.
    • Leaf: Represents leaf objects in the composition; doesn't have children; defines behavior for primitive objects.
    • Composite: Defines behaviors for components having children; stores child components; implements child-related operations in the component interface
    • Client: Manipulates objects in the composition through the component interface.

    UML DIAGRAM FOR COMPOSITE DESIGN PATTERN IMPLEMENTATION

    • Shown in the image will create an interface for " File ".
    • Will have two different classes one for directory type and second for classes other than directory (.txt, .doc, etc).

    IMPLEMENTING COMPOSITE DESIGN PATTERN IN JAVA

    • Example for file directory structure
    • Create child file and root directories.
    • Get size of files and directories

    COMPOSITE DESIGN PATTERN CLASS IMPLEMENTATION(JAVA)

    • Classes for file and directory types (e.g., TextFile, Directory)
    • Directory implements File and stores a list of File objects
    • TextFile implements File and has size

    APPLICATION CLASS (JAVA)

    • Implements main method for testing the code
    • Create TextFile objects child1 and child2
    • Create Directory object root
    • Add child1 and child2 to root
    • Print sizes of child1 and root.

    PROS AND CONS OF COMPOSITE PATTERN

    • Pros:
      • Data represented as a tree structure
      • Same operations on different object types
      • Reduces overhead for handling different types of objects
      • Open/Closed Principle: introducing new elements without breaking existing code
    • Cons:
      • Objects must be compatible
      • Complexity can increase

    DECORATOR PATTERN

    • Decorator is a structural design pattern that lets you attach new behaviors to objects by placing them inside special wrapper objects that contain the behaviors
    • Uses composition instead of inheritance to extend an object's functionality at runtime.
    • Also known as Wrapper
    • Wrap a component with any number of decorators (e.g., wrapping a gift, putting it in a box, wrapping the box).
    • Change component behavior by adding new functionality before and/or after method calls to the component
    • Provides an alternative to subclassing for expanding behavior

    WHERE CAN DECORATOR PATTERN BE USED?

    • Attach additional responsibilities to objects at runtime without altering code using these objects
    • Use when it's hard to extend object behavior with inheritance
    • Programming languages with the final keyword used to prevent further extension of a class

    UML CLASS DIAGRAM & PARTICIPANTS

    • Component: Defines an interface for objects that can have responsibilities added dynamically
    • Decorator: Decorators implement the same interface as the component; have a relationship with the object they extend (a has-a relationship).
    • ConcreteComponent: Object to be enhanced dynamically. Inherits from Component.
    • ConcreteDecorator: Decorators that enhance the state of the component, can add new methods, adding new behavior before or after existing methods.

    COFFEE SHOP EXAMPLE

    • Introduces a coffee shop, serving four beverage types (house blend, dark roast, decaf, espresso).
    • Starts by using inheritance but quickly realizes this leads to many classes for various combinations of beverages and condiments.
    • Example of "class explosion" caused by overuse of inheritance.
    • Suggests alternative approach to handle condiments.

    APPROACH 1

    • Add boolean variables in Beverage class to represent condiments (milk, soy, mocha, whip)
    • Override the cost method in specific concrete Beverage classes

    APPROACH 2

    • Use Decorator pattern to dynamically add condiments
    • Components are Beverage classes (DarkRoast, etc.)
    • Decorators are classes that add behavior to the Beverage object (e.g., Whip, Mocha)

    UML DIAGRAM OF DECORATOR PATTERN (EXAMPLE: MOCA AND WHIP DECORATIONS)

    • Graphic shows a DarkRoast class.
    • Shows how Mocha and Whip components add new behaviors, building up functionality

    DECORATOR PATTERN CLASS DEFINITION (EXAMPLE: MOCA CLASS)

    • Implments Beverage class
    • Has a beverage that it wraps

    IMPORTANT NOTE ON DECORATOR PATTERN

    • Decorator is a subclass of the Component class
    • You cannot create a ConcreteDecorator without a ConcreteComponent

    PROS AND CONS OF DECORATOR PATTERN

    • Pros:
      • Easily extend objects' behavior without creating subclasses.
      • Add and remove behaviors at runtime
      • Combine multiple behaviors using decorators.
    • Cons:
      • Hard to remove a specific decorator from the stack.
      • Code maintainability can be challenging as decorators can get numerous and similar; difficult to maintain and distinguish

    QUESTIONS

    • Composite: Composing Objects into Tree Structures
    • Decorator: Adding Behaviors to Objects by Placing them Inside Wrappers

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    Structural Design Patterns PDF

    Description

    Explore the Composite pattern, a key structural design pattern that allows the composition of objects into tree structures. This quiz will cover its principles, real-life applications like file systems and employee hierarchies, and how it enables uniform treatment of individual and composite objects.

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