Design Pattern Basic

Question 1

Types of design patters

Answer 1

Creational, Structural, Behavioral

Question 2

Creational

Answer 2

designed for class instantiation can be class or object creational patterns (e.g. singleton design)

Question 3

Structural

Answer 3

increase functionality of the classes involved without changing much of its composition (e.g. Decorator Design)

Question 4

Behavioral

Answer 4

take care of effective communication and the assignment of responsibilities between objects. Chain of responsibility, iterator, mediator, strategy

Question 5

Factory

Answer 5

a class handling creation of different object (e.g. ShapeFactory which returns different shape based on the info passed in) Used when a class cannot anticipate the type of objects it needs to create before hand. Allow creation of object without knowing the details of it.

Question 6

Abstract factory

Answer 6

A base class with abstract methods defining methods for the objects that should be created. Each factory class which derives the base class can create their own implementation of each object type.

Question 7

Aggregation

Answer 7

child can exits independently of the parent

Question 8

Composition

Answer 8

child cannot exist independent of the parent

Question 9

Singleton Pattern

Answer 9

is a creational design pattern that lets you ensure that a class has only one instance, while providing a global access point to this instance.
Code becomes so tightly coupled that you can't make changes without affecting everything associated with it. It also doesn't support inheritance and can be easily broken.

Question 10

Static Class

Answer 10

only provides static methods, does not provide an object

Question 11

Builder

Answer 11

builds complex object using simple objects step by step and use builder class to build the final object. It is a creational design pattern. (E.g. building a meal)

Question 12

Prototype pattern

Answer 12

Creational design patter that lets you copy existing objects without making your code dependent on their classes. E.g. when you want to copy an object but the some fields is private and can’t be accessed.

Question 13

Adapter Pattern

Answer 13

Bridge between two incompatible interface. Structural Design Pattern. E.g. MediaPlayer for MP3, MP4 files

Question 14

Bridge Pattern

Answer 14

is a structural design pattern that lets you split a large class or a set of closely related classes into two separate hierarchies—abstraction and implementation—which can be developed independently of each other. E.g. Remote and a set of devices

Question 15

Proxy

Answer 15

a class represents functionality of another class. It controls access to the original object. Have a concrete class and proxy class implementing same interface. The proxy class then contains the concrete class. It is a Structural design pattern. Similar to an API.

Question 16

Facade

Answer 16

hides complexities of the system and provides and interface the client using which the client can access the system. Structural Design Patter. Provide simplified interface to complex set of classes. E.g. You call to place an order through customer services. The customer service is the Facade.

Question 17

Decorator

Answer 17

allow user to add new functionality to an existing object without altering its structure. Create a decorator class which wraps the original class and provides additional functionality. It is a Structural Pattern. E.g. Donut adding chococlate

Question 18

Lazy Initialization

Answer 18

only initialize an object when it is needed

Question 19

Chain of responsibility

Answer 19

a behavioral design pattern that lets you pass requests along a chain of handlers. Upon receiving a request, each handler decides either to process the request or to pass it to the next handler in the chain. E.g. student submit applications and it’s passed through various handler to verify eligibility

Question 20

Iterator

Answer 20

is a behavioral design pattern that lets you traverse elements of a collection without exposing its underlying representation (list, stack, tree, etc.).

Question 21

Mediator

Answer 21

is a behavioral design pattern that lets you reduce chaotic dependencies between objects. The pattern restricts direct communications between the objects and forces them to collaborate only via a mediator object.

Question 22

State

Answer 22

is a behavioral design pattern that lets an object alter its behavior when its internal state changes. It appears as if the object changed its class. E.g. Document in different state(draft, published etc)

Question 23

Strategy

Answer 23

class behavior or its algorithm can be changed at run time. Creates object representing strategy, and then have a context which will store reference to a strategy. A behavioral design pattern that lets you define a family of algorithms, put each of them into a separate class, and make their objects interchangeable.

Question 24

MVC

Answer 24

model view controller. Separate application concerns. Model represent an object, view represent visualization and controller acts on both model and view. Controller control data flow into model and update view, it contains instance to the view and the model in its class.

Question 25

What are design patterns?

Answer 25

are typical solutions to commonly occurring problems in software design. They are like pre-made blueprints that you can customize to solve a recurring design problem in your code. These patterns save time and effort by employing dynamic aspects of object-oriented programming to allow user inputs to decide what outputs are displayed by rationalizing relationships between objects

Question 26

Explain the advantages of design patterns in Java

Answer 26

Design patterns provide a templated solution that can be used in multiple projects. I find this concept useful in defining the architecture of multiple systems and customizing them rather than coding everything by hand, over and over. I can also appreciate the thoroughness of the testing done to ensure these extensions are reliable and make my job substantially faster

Question 27

Factory vs Abstract Factory

Answer 27

“The primary difference between them is as follows: a factory pattern is a method of creating a single object through inheritance, while an abstract factory pattern creates factory patterns, effectively producing families of related objects.”