4.13: Java Examples

Temperature

The temperature program main function is listed twice, once using if-then-else and once using switch, followed by the supporting functions.

If Then Else

// This program asks the user to select Fahrenheit or Celsius conversion
// and input a given temperature. Then the program converts the given 
// temperature and displays the result.
//
// References:
//     https://www.mathsisfun.com/temperature-conversion.html
//     https://en.wikibooks.org/wiki/Java_Programming

import java.util.*;

public class Main {
    private static Scanner input = new Scanner(System.in);

    public static void main(String[] args) {
        String choice;
        
        choice = getChoice();
        if (choice.equals("C") || choice.equals("c")) {
            processCelsius();
        } 
        else if (choice.equals("F") || choice.equals("f")) {
            processFahrenheit();
        } 
        else {
            System.out.println("You must enter C to convert to Celsius or F to convert to Fahrenheit.");
        }
    }

Switch

    public static void main(String[] args) {
        String choice;
        
        choice = getChoice();
        switch (choice) {
            case "C":
            case "c":
                processCelsius();
                break;
            case "F":
            case "f":
                processFahrenheit();
                break;
            default:
                System.out.println("You must enter C to convert to Celsius or F to convert to Fahrenheit.");
        }
    }

Supporting Functions

    public static String getChoice() {
        String choice;
        
        System.out.println("Enter C to convert to Celsius or F to convert to Fahrenheit:");
        choice = input.nextLine();
        
        return choice;
    }
    
    public static void processCelsius() {
        double temperature;
        double result;
        
        temperature = getTemperature("Fahrenheit");
        result = calculateCelsius(temperature);
        displayResult(temperature, "Fahrenheit", result, "Celsius");
    }
    
    public static void processFahrenheit() {
        double temperature;
        double result;
        
        temperature = getTemperature("Celsius");
        result = calculateFahrenheit(temperature);
        displayResult(temperature, "Celsius", result, "Fahrenheit");
    }
    
    public static double getTemperature(String scale) {
        double temperature;
        
        System.out.println("Enter " + scale + " temperature:");
        temperature = input.nextDouble();
        
        return temperature;
    }

    public static double calculateCelsius(double fahrenheit) {
        double celsius;
        
        celsius = (fahrenheit - 32) * 5 / 9;
        
        return celsius;
    }
    
    public static double calculateFahrenheit(double celsius) {
        double fahrenheit;
        
        fahrenheit = celsius * 9 / 5 + 32;
        
        return fahrenheit;
    }
    
    public static void displayResult(double temperature, String fromScale, double result, String toScale) {
        System.out.println(Double.toString(temperature) + "° " + fromScale + " is " + result + "° " + toScale);
    }
}

Output

Enter C to convert to Celsius or F to convert to Fahrenheit:
 c
Enter Fahrenheit temperature:
 100
100.0° Fahrenheit is 37.77777777777778° Celsius

Enter C to convert to Celsius or F to convert to Fahrenheit:
 f
Enter Celsius temperature:
 100
100.0° Celsius is 212.0° Fahrenheit

Enter C to convert to Celsius or F to convert to Fahrenheit:
 x
You must enter C to convert to Celsius or F to convert to Fahrenheit.

References

• Wikiversity: Computer Programming