RPN calculator

The RPN calculator implementation is a good exercise for working through a languages capabilities and exploring OO strategies.

I have done four variations of the RPN calculator as exploratory into languages:

• java
• scala
• javascript / node.js
• python

How to run

This implementation utilizes Java and Gradle.

Prereqs

To install Java and Gradle, either download or install using brew

brew install java
brew install gradle

Unit Test

To run the tests, run the following command:

gradle test

To add a new operator

1. Create a new operator implementation class. Add this class to the operators directory. Follow the conventation of (operator name)-operator.js (example: addition-operator.js).

2. The operator implementation class needs to implement the interface Operator, which will have the class implement the following methods

• doOperation(RpnStack): this method is responsible for pop-ing the operands from the stack, execute the operation, and push the result back to the stack
• handlesOperatorCharacter(String): this method is responsible for checking if this class handles a particular operator character. For example, an addition operation class would return true for +.

A sample base implementation for addition is shown below:

public class AdditionOperator implements Operator {

    private static final String PLUS = "+";

    @Override
    public int doOperation(RpnStack numbers) {
        int rhs = numbers.pop();
        int lhs = numbers.pop();
        int result = rhs + lhs;
        numbers.push(result);
        return result;
    }

    @Override
    public boolean handlesOperatorCharacter(String operand) {
        return PLUS.contentEquals( operand );
    }

}

3. Register operator in OperatorRegistry. To do this, add the following statement:

operatorRegistry.add( new AdditionOperator() );