This repository details the creation of a primitive flat file database system using scheduled threads and how to use it.
As of now, the database accepts five basic commands:
CREATE TABLE <table_name> (column1,column 2,column 3,....)
SELECT column1,column2,column3,.... FROM <table_name>
INSERT INTO <table_name> (value1,value2,....)
DROP TABLE <table_name>
EXIT, to terminate the program
Therefore, the user can create as many tables as s/he wants, insert values for whatever table s/he wants, and can select any number of columns from an individual table.
For example, two tables can be created, and the user can insert and select information in a sequence such as the one below:
-
CREATE TABLE person (name,phone,age) -
INSERT INTO person (john,7734566474,35) -
INSERT INTO person (mary,3124567343,28) -
CREATE TABLE company (name,phone,address) -
INSERT INTO company (Pepsico,37927392,12 Quaker St.) -
INSERT INTO company (M&M,23423422,987 Mars st.) -
INSERT INTO person (kim,8475675849,30) -
SELECT name,address FROM company -
DROP TABLE person -
EXIT
Keep in mind, that this is an example and the queries can be executed in whichever order the user likes.
As the user continues to add information to different tables - or remove tables - within their database, the database is continuously rebuilt and written into a file in the same directory as the project and saved under MyDatabase.txt. This is done through the use of a scheduled thread.
Finally, the user interacts with this program via their command line interface.
Dependency Injection is used as the primary programming technique for this software.
The design is described as follows:
A Database object depends on different Tables, and each Table consists of an n amount Rows. Each row is inherently able to hold an n amount of elements according to how the user specifies his or her tables.
The advantages of this are:
- Decoupling the creation of objects (in other word, separate usage from the creation of object).
- Ability to replace dependencies (i.e., Table or Row) without changing the class that uses it (Database).
- Promotes the "code to interface not to implementation" principle if applicable.
- Ability to create and use mock dependency during test.
An inner class called Projection is utilized inside of the Table class as a mechanism of security. Like a normal relational database management system (RDBMS) such as MySQL, users cannot explicitly create their own projections of certain columns within a table. This can only be done through the use of the "SELECT" keyword. Thus, the when a user selects certain columns of a table to be viewed, a Projection object is created within the Table class, which is then printed out to the console.
Finally, a number of lambda and stream expressions are used within this project. The scheduled thread in the Main class and the overridden toString() method in the Database class were viable candidates to utilize lambdas and/or streams within the project.
The easiest way to run this program is to clone the project and run the main method of Main.java through an integrated development environment like IntelliJ. Then, you will be able to interact with the program through its terminal.