Design Patterns

Question 1

What is a factory?

Answer 1

method that wraps a constructor/methods that create objects

Question 2

what is an abstract factory?

Answer 2

method that creates objects and doesn’t specify class

Question 3

what is a builder?

Answer 3

object that can create other objects, can store configurations

Question 4

what is an injector?

Answer 4

creates/imports target objects and injects them into the target object during creation. Thus, the target object does not create its has-a fields

Question 5

what is lazy initiation?

Answer 5

defer creating an object until absolutely necessary, commonly a pointer stores the reference to the object and it set to null in the beginning

Question 6

what is singleton?

Answer 6

only one object for a class. shared across thread/tasks

Question 7

what is multiton?

Answer 7

multiple but finite objects for a class, stored in a collection (e.g. map) controlled access/allocation

Question 8

what is an adapter?

Answer 8

converts an interface to another and connects two systems, useful when not possible to change existing structures

Question 9

what is a bridge?

Answer 9

allows implementations to vary, allows objects to vary

Question 10

what is a composite?

Answer 10

enables treating members of trees (or graphs) in the same way regardless if there are terminal, middle roots, etc.

Question 11

what is a twin?

Answer 11

work around for multiple inheritance, clients refer only to one of the two objects directly, depending on their design. Interfaces could be used for further abstraction. Multi-implementation of interfaces is normally allowed.

Question 12

what is an iterator?

Answer 12

go through all elements of a collection and run a method on each

Question 13

what is a thread pool?

Answer 13

creates N threads, add tasks in the pools queue and each thread taks the next task from the queue and runs it.

Question 14

what is read/write lock

Answer 14

allows only one writer to lock and multiple readers can read