Interfaces, Contracts and Protocols

Question 1

What is an interface?

Answer 1

An interface is a description of the actions that an object can do.

A set of behaviours.

A contract between the object & things that are using/implementing that object.

Imagine a vehicle. It can turn left/right & drive forwards/backwards. You don’t care how, just that is does.

In Object Oriented Programming, an Interface is a description of all functions that an object must have in order to be an ”X”

Question 2

Why should should interface be used?

Answer 2

To organising functionality into relevant and focused behaviours.

It can function as a contract within development teams
- Helps abstracting & generalising your code - for other users/programmers

It makes your code scalable & flexible when coding towards interfaces and not implementation.

To minimise the cost of change & maintenance.

Useful when testing.

• (read first 6 lines if u can’t remember what pros there are about abstraction -
  (https: //stackify.com/oop-concept-abstraction/))

Question 3

What is an interface not?

Answer 3

A class that contains constructors - rather it is implemented by classes.

Able to be instantiated

Able to contain anything else than method signatures
and constants, static, final fields

Able to be extended by a class - it is implemented by other classes/interfaces

Question 4

Is and interface extended or implemented by a class?

Answer 4

It is implemented.

Question 5

Mention some main protocols use in the File Transfer pattern.

Answer 5

HTTP/HTTPS, FTP, SFTP/SCP

all based on client/server architecture.

Question 6

What is HTTP?

Answer 6

Typer Text Transfer Protocol - application layer protocol.

HTTP can fetch resources like HTML, CSS, JSON, XML etc via the request/response pattern.

HTTP is connection-less, mediaindependent & stateless.

HTTPS is the common use for web servers since it adds SSH security.

Question 7

What is FTP?

Answer 7

File Transfer Protocol.

It is and old protocol & should not be used since it uses “clear text” password (unencrypted).

FTP is stateful meaning that it will maintain state information like a user’s current directory.

Question 8

What is SFTP?

Answer 8

Secure File Transfer Protocol.

replaces FTP & adds an extra layer of security (through SSH) to FTP.