Week 8

Question 1

What is the Decorator Pattern?

Answer 1

The Decorator Pattern attaches additional behavioral responsibilities to an object dynamically, providing a flexible alternative to subclassing for extending functionality

Question 2

What problem does the Decorator Pattern solve in the coffee shop example?

Answer 2

It avoids class explosion caused by subclassing every possible combination of coffee and condiments by dynamically adding condiments as decorators

Question 3

What are the key principles behind the Decorator Pattern?

Answer 3

1. Code should be open for extension but closed for modification (Open-Closed Principle)
2. Favor object composition over class inheritance

Question 4

What are the components of the Decorator Pattern?

Answer 4

1. Component: Defines an interface for objects.
2. ConcreteComponent: Implements the Component interface.
3. Decorator: Wraps a Component and modifies its behavior.
4. ConcreteDecorator: Adds new responsibilities to the Component.

Question 5

How are condiments added in the Decorator Pattern?

Answer 5

Condiments are treated as decorators that wrap the base beverage. Each decorator adds its own cost and description

Question 6

What is the Command Pattern?

Answer 6

The Command Pattern encapsulates a request as an object, allowing it to parameterize objects with requests, queue requests, or support undoable operations

Question 7

What are the main roles in the Command Pattern?

Answer 7

1. Invoker: Holds and triggers the command
2. Command: Declares an interface for executing actions
3. ConcreteCommand: Binds a receiver to an action
4. Receiver: Performs the action
5. Client: Configures the ConcreteCommand and assigns the Receiver

Question 8

How does the Command Pattern apply to a remote control example?

Answer 8

Each button on the remote control acts as an Invoker, sending requests encapsulated in ConcreteCommands to corresponding Receivers (e.g., lights, garage doors).

Question 9

What are the advantages of the Command Pattern?

Answer 9

1.Decouples sender and receiver.

2. Supports queuing and logging requests.
3. Enables undo functionality.

Question 10

What are examples of the patterns covered in the lecture?

Answer 10

1. Decorator Pattern: Dynamically extends functionality
2. Command Pattern: Encapsulates requests as objects

Question 11

What are the key OO design principles supporting these patterns?

Answer 11

1. Encapsulate what varies.
2. Program to an interface, not an implementation
3. Favor object composition over inheritance
4. Classes should be open for extension but closed for modification
5. Depend upon abstractions, not concrete classes (Dependency Inversion Principle)

Question 12

What is the “Open-Closed Principle”?

Answer 12

A design principle stating that classes should be open for extension but closed for modification

Question 13

What is dynamic runtime decoration in the Decorator Pattern?

Answer 13

Objects can be decorated at any time, allowing behavior to be dynamically added during program execution

Question 14

What is an example of dynamic decoration in Java?

Answer 14

Wrapping a DarkRoast object with Mocha and Whip decorators to compute the total cost dynamically.

Question 15

What are some limitations of the Decorator Pattern?

Answer 15

1. Introduces new levels of abstraction.
2. Can make the object composition more complex and harder to manage.

Question 16

What is Java Generics?

Answer 16

Java Generics, introduced in Java 5.0, add stability by enabling compile-time type checking and reducing runtime errors caused by incorrect type casting

Question 17

Why use Java Generics?

Answer 17

Facilitates generic programming, allowing algorithms to be written for unspecified types

Enables type-safe code reuse

Detects potential runtime errors at compile time

Question 18

What is a generic container?

Answer 18

A container class with a type variable (e.g., T) allowing the use of specific types without needing explicit casting

Question 19

What are the naming conventions for type parameters?

Answer 19

Common type parameter names:

E – Element
K – Key
N – Number
T – Type
V – Value
S, U, V – Secondary types

Question 20

What are the types of generics in Java?

Answer 20

Generic Types

Generic Methods

Generic Constructors

Question 21

What is type inference in methods?

Answer 21

Type can be inferred without explicit specification if the compiler can deduce it from the context (e.g., using diamonds < > introduced in Java 7)

Question 22

What are bounded types?

Answer 22

Allows restricting type parameters:

Upper bound: <T></T>

Lower bound: <T></T>

Question 23

What is the role of wildcards (?)?

Answer 23

Represent unknown types, enabling flexibility:

Upper bound: <? extends Type>

Lower bound: <? super Type>

Question 24

What is type erasure?

Answer 24

Type information is removed during compilation to ensure backward compatibility

Generic types exist only at compile time and are replaced by raw types at runtime

Question 25

Why should legacy and generic types not be mixed?

Answer 25

Mixing can lead to warnings about unchecked or unsafe operations and negate the safety benefits of generics

Question 26

What is heap pollution?

Answer 26

Occurs when a variable of a parameterized type refers to an instance of an incompatible type

Often results in unchecked warnings

Question 27

What are the benefits of using Java Generics?

Answer 27

Stronger compile-time type checks

Elimination of explicit casting

Simplified and type-safe code