Applied Programming/Conditions/Java

conditions.java

/** 
 * This program converts a Fahrenheit temperature to Celsius.
 * 
 * Input:
 *     Fahrenheit temperature
 * 
 * Output:
 *     Fahrenheit temperature
 *     Celsius temperature
 * 
 * Example:
 *     Enter Fahrenheit temperature:
 *      100
 *     100.0° Fahrenheit is 37.8° Celsius
 * 
 * References:
 *     * http://sphinxcontrib-napoleon.readthedocs.io/en/latest/example_google.html
 *     * https://www.w3resource.com/slides/java-coding-style-guide.php
 *     * https://en.wikipedia.org/wiki/Javadoc
 *     * http://www.mathsisfun.com/temperature-conversion.html
 */

import java.util.Scanner;

/**
 * Runs main program logic.
 */
class Main {
    public static final double ABSOLUTE_ZERO = -459.67;
    public static final int TEMPERATURE_DIFFERENCE = 32;
    public static final double TEMPERATURE_RATIO = 5.0 / 9;

    public static void main(String[] args) {
        try {
            double fahrenheit = getFahrenheit();
            double celsius = fahrenheitToCelsius(fahrenheit);
            displayResults(fahrenheit, celsius);
        }
        catch (Exception exception) {
            System.out.println("Unexpected error.");
            exception.printStackTrace();
        }
    }
    
    /**
     * Gets Fahrenheit temperature.
     * 
     * @return  Fahrenheit temperature
     * 
     * Exits:
     *      If Fahrenheit temperature is not a valid float.
     *      If Fahrenheit temperature is below absolute zero.
    */
    private static double getFahrenheit() {
        try {
            System.out.println("Enter Fahrenheit temperature:");
            Scanner scanner = new Scanner(System.in);
            double fahrenheit;
            fahrenheit = scanner.nextDouble();
            if (fahrenheit < ABSOLUTE_ZERO) {
                System.out.println("Fahrenheit temperature cannot be below absolute zero.");
                System.out.println("Temperature is invalid.");
                System.exit(0);
            }
            return fahrenheit;
        }
        catch (java.util.InputMismatchException exception) {
            System.out.println("Fahrenheit temperature must be a floating point value.");
            System.out.println("InputMismatchException: Temperature is invalid.");
            System.exit(0);
            return 0;
        }
    }
    
    /**
     * Converts Fahrenheit temperature to Celsius.
     * 
     * @param   Fahrenheit temperature
     * @return  Celsius temperature
     * @throws  IllegalArgumentException if temperature is below absolute zero
    */
    private static double fahrenheitToCelsius(double fahrenheit) {
        if (fahrenheit < ABSOLUTE_ZERO) {
            throw new IllegalArgumentException(
                "fahrenheit must not be below absolute zero.");
        }
        double celsius;
        celsius = (fahrenheit - TEMPERATURE_DIFFERENCE) * TEMPERATURE_RATIO;
        return celsius;
    }
    
    /**
     * Displays Fahrenheit and Celsius temperatures.
     * 
     * @param   Fahrenheit temperature
     * @param   Celsius temperature
     * @throws  AssertionError if fahrenheit less than absolute zero
     * @throws  AssertionError if celsius is less than absolute zero
    */
    private static void displayResults(double fahrenheit, double celsius) {
        assert fahrenheit >= ABSOLUTE_ZERO : "fahrenheit less than absolute zero";
        assert celsius >= fahrenheitToCelsius(ABSOLUTE_ZERO) : 
            "celsius less than absolute zero";
        System.out.println(String.format(
            "%1$.1f° Fahrenheit is %2$.1f° Celsius",
            fahrenheit,
            celsius));
    }
}
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conditions.java

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See Also
