Lecture 10-11

Question 1

Where did design patterns originate from?

Answer 1

Design patterns originated from recurring themes in planning and building architecture.

Question 2

What is a creational pattern in design patterns?

Answer 2

A pattern that deals with object creation mechanisms.

Question 3

What is the Singleton pattern?

Answer 3

A creational pattern that ensures a class has only one instance and provides a global point of access to that instance.

Example: We want only one instance of a class (such as a Scanner or Logger class)

Question 4

What is the purpose of the Singleton pattern?

Answer 4

To ensure a class only has one instance for the duration of the system.

Question 5

What is an example of a problem that the Singleton pattern solves?

Answer 5

Ensuring there is only one instance of a Scanner or Logger class.

Question 6

What is the Factory Method pattern?

Answer 6

A creational pattern that defines an interface for creating an object, but lets subclasses decide which class to instantiate.

Question 7

What is an example application of the Factory Method pattern?

Answer 7

A superclass Animal with a makeNoise() method, and subclasses like Cow, Dog, and Cat that implement the makeNoise() method differently.

Question 8

What are structural patterns concerned with?

Answer 8

How classes and objects can be composed to form larger structures.

Question 9

What do structural patterns focus on?

Answer 9

How classes inherit from each other and how they are composed from other classes.

Question 10

What is the Adapter pattern?

Answer 10

A structural pattern that allows incompatible interfaces to work together without modifying their existing code.

Question 11

What is an example of the Adapter pattern?

Answer 11

Two F1 temperature sensors with incompatible temp-reporting methods, or the travel electricity socket problem with Euro and Australian socket plugs.

Question 12

What is the intent of the Adapter pattern?

Answer 12

To convert the interface of a class into another interface that the client expects.

Question 13

What is the Composite pattern?

Answer 13

A structural pattern that composes objects into tree structures to represent whole-part hierarchies.

Question 14

What is the applicability of the Composite pattern?

Answer 14

When you want to represent whole-part hierarchies of objects.

Question 15

What is the Observer pattern?

Answer 15

A behavioral pattern where when a particular object in the system changes its state, other ‘subscribed’ objects are notified and updated automatically.

Question 16

What is the intent of the Observer pattern?

Answer 16

To define a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.

Question 17

When should the Observer pattern be used?

Answer 17

When a change to one object requires changing others, or when an object should be able to notify other objects without making assumptions about those objects.

Question 18

What problem does the Singleton pattern commonly solve?

Answer 18

Ensuring only one instance of a class, such as a Scanner or Logger class, is created.

Question 19

What must be true for a class to use the Singleton pattern?

Answer 19

There must be exactly one instance of the class, and it must be accessible from a well-known access point.

Question 20

What does the Factory Method pattern allow subclasses to do?

Answer 20

Decide which class to instantiate when creating an object.

Question 21

What are the 3 categories of Design Patterns

Answer 21

1. Creational Pattern
2. Structural Pattern
3. Behavioural Pattern

Question 22

Give 2 examples of a Structural Pattern

Answer 22

1. Adapter Pattern
2. Composite Pattern

Question 23

Give 2 examples of a Creational Pattern

Answer 23

1. Singleton
2. Factory Method

Question 24

Give 2 examples of a Behavioural Pattern

Answer 24

1. Observer Pattern
2. Strategy Pattern