OO

Question 1

What’s the difference between a parameter and an argument?

Answer 1

Parameters don’t have value, they are just the names of the inputs in function/method definition while arguments are the values passed in for the parameters when function/method is called

Question 2

Explain why you should “encapsulate what varies”

Answer 2

Separating what changes frequently from what stays the same frequently prevents having to rewrite logic every time a new type of change is introduced.

Question 3

Program to a ____ not a ____

Answer 3

interface | implementation

Question 4

Why is it preferred to program to an interface and not an implementation?

Answer 4

Allows implementation to change/improve, without affecting clients.

Question 5

Complete the design principle: Encapsulate what ___

Answer 5

varies

Question 6

Complete the design principle: Favor ____ over ____

Answer 6

composition | inheritance

Question 7

Why is composition usually preferred over inheritance.

Answer 7

Allows for loose coupling. Can get many of same benefits of inheritance (reuse attributes, methods) but with more flexibility to behave differently.

Question 8

“Has a” defines what kind of relationship?

Answer 8

Composition

Question 9

“Is a” implies what kind of relationship?

Answer 9

Inheritance

Question 10

Define Aggregation

Answer 10

Comprised of one or more of something, in a “has a” relationship. Still is a thing if it loses all those somethings.

Question 11

What is composition?

Answer 11

When an object is comprised of one more more of something else in a “has a” relationship.

Question 12

Explain the single responsibility principle.

Answer 12

Class should only have one reason to change because every additional responsibility increases the chance of change, and we want to minimize code changes (prefer code additions).

Question 13

What is the idea behind loose coupling?

Answer 13

Composition is loose coupling, inheritance is strong coupling. Loose coupling is often more flexible.

Question 14

What is the open closed principle?

Answer 14

Open for extension but close for modification. Should be able to augment an object without opening up its code, decorator a good example of this.

Question 15

Explain the strategy pattern.

Answer 15

If a certain aspect of something can change a lot, or would change in the future, encapsulate what varies and place the business logic in something else, which can be a component of the original object.

Question 16

Explain the adapter pattern.

Answer 16

Think of a electrical socket adapter. The device has no idea it’s using an adapter, the socket has no idea what’s plugged in is an adapter. You can make a work with b by making a c, rather than modifying a or b. Good for when libraries are changed.

Question 17

Explain the observer pattern.

Answer 17

One to many dependency. One thing keeps track of state, other objects can register themselves with the observer. When state changes, observer notifies all registered objects.

Question 18

Explain the iterator pattern

Answer 18

Iterator is essentially an agreed upon interface in a particular language, so any type that implements it can be iterated through in a consistent manner, regardless of what the underlying implementation looks like.

Question 19

Explain the decorator pattern.

Answer 19

Wrap something up to provide additional logic or attributes. Can be done infinitely. Rather than have a million different attributes and stuff to denote coffee types, have coffee be wrapped up in with whip, with sugar. Each wrapper should behave like a regular coffee type, and contain what its wrapping up.

Question 20

What does it mean that a function has side effects?

Answer 20

It doesn’t return anything. Maybe it alters an array or writes to a file, or prints to screen, etc

Question 21

What is a pure function?

Answer 21

Always will return the same output, given the same input, every time.

Question 22

What’s the difference between a method and a function (at least in Python)?

Answer 22

Method is a function that belongs to an object. Function is it’s own independent object.

Question 23

True or false, you should define all instance attributes of an object in its constructor?

Answer 23

True. Otherwise someone may try to access an attribute that has not yet been set by a method. Can initialize to null or None.