/bfh-kotlin-calculator

Primary LanguageJava

Rational Calculator

Introduction

The goal of this exercise is to implement a calculator that allows you to make exact calculations with rational numbers. A rational number consists of a numerator and a denominator separated by a slash, e.g. 2/3. Allowed operations are additions (+), subtractions (-), multiplications (*), and divisions (:). The result of a calculation shall always be reduced, e.g. the result of 1/2 + 1/6 is 2/3.

Rational Number Class

Implement an immutable and final class RationalNumber which represents rational numbers.

The class has two constructors, one which takes only the numerator as argument (the denominator is set to 1), and one which takes the numerator and denominator as arguments (an IllegalArgumentException is thrown if the denominator is 0). The latter constructor reduces and normalizes the numerator and denominator such that their greatest common divisor is 1 and the denominator is positive.

@Kotlin: Use an Init-Block to validate the parameters of the constructor and to reduce and normalize the numerator and denominator.

Furthermore, the class provides the following methods:

  • getNumerator and getDenominator to obtain the numerator and denominator of the rational number
  • negative and reciprocal to calculate the negative and reciprocal of the rational number
  • add, subtract, multiply and divide which take another rational number as argument and return the sum, difference, product and quotient of the two numbers
  • equals, hashCode and toString to test if the rational number is equal to another one, and to create a hash code or a string representation of the rational number

Use the test class RationalNumberTest to verify your implementation.

Rational Calculator Class

Implement a class RationalCalculator which allows a user to perform rational calculations. The class has the following the static methods:

  • The convert method takes a string representing a rational number and returns the corresponding RationalNumber object. Hint: Create a Scanner object on the string, set / as delimiter and use the nextIntmethod to obtain the numerator and denominator.
  • The evaluate method takes a string representing of a rational expression and returns its value as RationalNumber object. Hint: Create a Scanner object on the string and use the next method with the regex patterns -?[0-9]+(/-?[0-9]+)? and [+\\-*:] to obtain the next rational number or operator (see class java.util.regex.Pattern) for a description of the regex syntax)
  • The main method repeatedly prompts the user to enter a rational expression and displays its value, e.g.
> 1 + 1/2
3/2
> 1 + 1/2 - 1/6
4/3
> 1 + 1/2 - 1/6 * 1/4
1/3
> 1 + 1/2 - 1/6 * 1/4 : 1/3
1

Use the test class RationalCalculatorTest to verify your implementation.

@Kotlin: Kotlin does not know static methods, use top level functions instead. To be called correctly from the test class, insert the following annotation into your Kotlin file (as the first line):

@file:JvmName("RationalCalculator")

Remarks

<rational_expression> ::= <rational_number> | <rational_expression> " " <operator> " " <rational_number>
<rational_number> ::= <integer> "/" <integer>
<integer> ::= <unsigned_integer> | "-" <unsigned_integer>
<unsigned_integer> ::= <digit> | <digit> <unsigned_integer>
<digit> ::= "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9"
<operator> ::= "+" | "-" | "*" | ":"
  • If an input line does not contain a valid expression, a corresponding error message shall be displayed.
  • The expressions are evaluated from left to right without regard to an operator precedence.

Extra Task

The test class RationalNumberTest uses random numbers between 0 and 1000. If this bound is removed, the tests will often fail. Why is that and how could this behavior be corrected?