## Questions People have Asked Me – Part 1

Below are some questions I was recently asked, with my answers.

Please let me know if any of them are wrong, its a learning opportunity for me 🙂

What is the binary sort algorithm and how does it work?

The binary sort algorithm (BSA) is used to effectively sort data. It works on the principle of continuously cutting the data set in half, until it finds what it is searching for. However, this algorithm only works on data sets that are already sorted.

First the BSA checks the middle of the data set and compares the value it is searching for. If this value is the value it is searching for then it stops. However, if it is not equal, it checks if the value it found is bigger or smaller then the value it is trying to find. If the value is smaller, the BSA repeats the process on the left, whereas if the value is bigger it repeats the process on the right. This process is repeated multiple times until the value that the BSA is looking for is found.

What is recursion and how is it used?

Recursion in programming is when the program starts calling its self, from inside its self. This programming technique is usually used when a single large program can be solved in smaller parts and has a valid base case. Such as computing the Fibonacci Sequence or traversing a binary search tree.

What is polymorphism and what is its purpose?

Polymorphism is an aspect of Object-Oriented Programming where a “object” can take on many different forms, if all the forms are its children.

Explain when you should use interfaces and when you should use abstract base classes.

Both interfaces and abstract classes are a type of contract, in the class structures of a software application. Interfaces are a form of contract between two different entities, where you want to separate the functions from the implementations. This is done such that you existing application does not need to change much if a certain part of it is changed. This can be seen in the commonly used repository pattern, which is used to separate data access logic from the business logic. Where as abstract classes are a less extreme version of interfaces, where certain methods defined in it can have real implementations. This allows any child class that inherits from the abstract class to get those method implementations. The difference between the two can be further seen in how their child methods are derived. Since interfaces are “implemented”, where as abstract classes are “extended”.

When should you use static methods and static variables? And when shouldn’t you use them.

Static methods and variables can be used from a class without having to instantiate it. This is usually used when, you want to group a set of functionality or utility function together. An example of this is the “Math” class in JAVA, which gives the user all the math related function they need. You wouldn’t want to use them when you would be creating your inheritance-based class structures, most of the time.

Write a SQL statement to create a table called “author” with the columns “id”, “name”, “age” (for MySQL or SQL Server).

CREATE TABLE author (

id int NOT NULL AUTO_INCREMENT,

name varchar(255) NOT NULL,

age int,

PRIMARY KEY (id)

);

Write a SQL statement to create a table called “book” with the columns “id”, “title”, “genre”, “author_id” (for MySQL or SQL Server).

CREATE TABLE book (

id int NOT NULL AUTO_INCREMENT,

title varchar(255) NOT NULL,

genre varchar(255),

author_id int,

PRIMARY KEY (id),

FOREIGN KEY (`author_id`) REFERENCES `author` (`id`) ON DELETE CASCADE);

For the “author” and “book” tables created above, write a SQL statement to tell you the number of books each author has written, but only for authors who have written 2 or more books. The output should not show authors that have written only 1 book. The output should have the author’s name and the number of books they have written.

SELECT author.name, COUNT(*) AS ‘# books’ FROM author, book WHERE author.id = book.author_id GROUP BY author.name HAVING COUNT(*) > 1;

In databases, what are indexes used for and how to you decided how to use them effectively.

Indexes in databases are used to speed up data retrieval. However, they come at the additional cost of space, and added complexity to database maintenance. They should only ever be used when the same type, or group of data is constantly being accessed. If the number of reads get even larger, there should also be some sort of caching layer the application queries, such that it doesn’t need to query the SQL database directly.

What is the value of unit testing and what are some of your strategies for writing good unit tests?

Unit testing is used to test the functionality of the different parts of an application. Its value lies in the fact that they make the programmer, test their code in a systematic way. And feeds into a workflow where tests are run before anything gets committed to the master branch. I think the best way to write a test case, is to write the test before writing the application logic, since it gets you thinking about what edge/special cases to consider. This is also known as the test-driven development approach.