java-calculator

A calculator (console application) built with Java

Description

This application allows the user to input verbal math expressions and gets the results using Syntax Tree.

Available operators:

• plus
• minus
• times
• divided

Samples:

Input	Result
1 plus 3 minus 4	0
(1 plus 3) times 4	16
2 plus (5 plus (2 times 7))	21
1 plus 1	2
1000 minus 1	999
2 plus 1 minus 5 divided 2 minus 1	-0.5
4 times 4	16
20 divided 5	4
0.5 times 10	5

Please, check the Implementation section for more details.

Requirements

For local usage:

• Java 15.0.1-zulu

Running

Be sure to install the requirements. If using sdkman, you can easily run:

sdk install java 15.0.1-zulu

Now, open your favorite IDE to open this project and use the "Run" button.

I recommend IntelliJ IDEA, but fell free to use other IDE.

Here is how it can be used:

Implementation

This application uses stdin and stdout as an entry point for the system (just because this way is more simple than implementing a REST API).

How does it work?

Let's considerate this expression:

2 plus 5 times 3

1. Given the expression;
2. Convert the original expression into a list of tokens:
3. Parse the tokens, respecting the order of the operators (precedence), to calculate the final result.

• It's required to follow the math concept of BODMAS. Here is an article about BODMAS. In resume:
  • Do things in Parentheses First
  • Multiply or Divide before you Add or Subtract
  • Otherwise just go left to right