Array in Java with command line

Question

I'm doing a project with command line and array. A program that converts F -> C and C -> F. Here what I got so far:

public class Implementation 
{
    public static void main(String[] args)
    {        
        double degree = 0;
        String celsius = null;
        String fahrenheit; 
        int n = 0;
        String[] days = {"Very Cold", "Cold", "Mild", "Very Mild", "Warm", "Very Warm", "Hot"};       
            if (degree < 0)
            {    
            n = 0;
            }
            if (degree >= 0 && degree < 32)
            {    
            n = 1;
            }
            if (degree >= 32 && degree < 50)
            {    
            n = 2;
            }
            if (degree >= 50 && degree < 60)
            {    
            n = 3;
            }
            if (degree >= 60 && degree < 70)
            {    
            n = 4;
            }
            if (degree >= 70 && degree < 90)
            {    
            n = 5;
            }
            if (degree >= 90)
            {    
            n = 6;
            }   
        if (args.length != 3)
        {
            System.out.println("Error! Please try again.");
            System.exit(0);
        }
        else
        {

            degree = Double.parseDouble(args[0]);
            celsius = args[1]; 
            fahrenheit = args[2];        
        }

        switch (celsius)    
        {
            case "c":
            System.out.printf("%n%s Celsius is %.5s Fahrenheit %s\n", args[0], fahrenheit(degree), days[n]);
            break;
            case "f":
            System.out.printf("%n%s Fahrenheit is %.5s Celsius %s\n", args[0], celsius(degree), days[n]);
            break;
        }
    }
    public static double celsius(double fahrenheitTemperature)
    {
        return ( 5.0 / 9.0 * ((double) fahrenheitTemperature - 32));
    }
    public static double fahrenheit(double celsiusTemperature)
    {
    return  ( 9.0 / 5.0 * (double) celsiusTemperature + 32);
    }
}

I have problem in Array part. I couldn't get the right array days[] with the specific degree. For example, If I do command line: 100 cf , it supposes to show up 100 Celsius is 212.0 Fahrenheit Cold "Hot" . But my program only shows up "Cold" , no matter what degree I input.

Answer 1

you set

double degree = 0;

then

String[] days = {"Very Cold", "Cold", "Mild", "Very Mild", "Warm", "Very Warm", "Hot"};    

so of course it will result in "Cold" all the time ...

Here is a fully working class:

As you can see in my solution the whole point is to create a function which returns the proper integer , depending on the degree you provide as input .. this function is called public static int checkDegree(double degree) { . This way you put the functionality in a function and remove it from the main class (which is very problematic the way you had it) . this way you call the function as an argument directly, and the function gives you proper days you need for the logic you request , instead of calling the days[n] directly , which was causing the troubles you were faced with in the first place...

public class Implementation 
{
    public static void main(String[] args)
    {        
        double degree=0;
        String celsius=null;
        String fahrenheit;
        int n;
        String[] days = {"Very Cold", "Cold", "Mild", "Very Mild", "Warm", "Very Warm", "Hot"}; 
        if (args.length != 3)
        {
            System.out.println("Error! Please try again.");
            System.exit(0);
        }
        else
        {
            degree = Double.parseDouble(args[0]);
            celsius = args[1]; 
            fahrenheit = args[2];        
        }

        switch (celsius)    
        {
            case "c":    
            System.out.printf("%n%s Celsius is %.5s Fahrenheit %s\n", args[0], fahrenheit(degree), days[checkDegree(degree)]);
            break;
            case "f":
            System.out.printf("%n%s Fahrenheit is %.5s Celsius %s\n", args[0], celsius(degree), days[checkDegree(degree)]);
            break;
        }
    }
    public static double celsius(double fahrenheitTemperature)
    {
        return ( 5.0 / 9.0 * ((double) fahrenheitTemperature - 32));
    }
    public static double fahrenheit(double celsiusTemperature)
    {
    return  ( 9.0 / 5.0 * (double) celsiusTemperature + 32);
    }
    public static int checkDegree(double degree) {
        int myReturn = 0;
        if (degree < 0)
            {    
            myReturn = 0;
            }
            if (degree >= 0 && degree < 32)
            {    
            myReturn = 1;
            }
            if (degree >= 32 && degree < 50)
            {    
            myReturn = 2;
            }
            if (degree >= 50 && degree < 60)
            {    
            myReturn = 3;
            }
            if (degree >= 60 && degree < 70)
            {    
            myReturn = 4;
            }
            if (degree >= 70 && degree < 90)
            {    
            myReturn = 5;
            }
            if (degree >= 90)
            {    
            myReturn = 6;
            }   
            return myReturn;
    }
}

INPUT : java Implementation 100 cf

OUTPUT : 100 Celsius is 212.0 Fahrenheit Hot

Answer 2

Your

double degree = 0;

remains always 0. You change it after your if statements so it is always 0.

You can change this:

switch (celsius)    
        {
            case "c":
            System.out.printf("%n%s Celsius is %.5s Fahrenheit %s\n", args[0], fahrenheit(degree), days[n]);
            break;
            case "f":
            System.out.printf("%n%s Fahrenheit is %.5s Celsius %s\n", args[0], celsius(degree), days[n]);
            break;
        }

to this:

switch (celsius)    
        {
            case "c":
            System.out.printf("%n%s Celsius is %.5s Fahrenheit ", args[0], fahrenheit(degree));
            break;
            case "f":
            System.out.printf("%n%s Fahrenheit is %.5s Celsius ", args[0], celsius(degree));
            break;
        }

and move it just right above your degrees declaration. Move this part too:

if (args.length != 3)
        {
            System.out.println("Error! Please try again.");
            System.exit(0);
        }
        else
        {

            degree = Double.parseDouble(args[0]);
            celsius = args[1]; 
            fahrenheit = args[2];        
        }

Then at the end of your main() add this:

System.out.printf("%s\n", days[n]);

That's the quickest fix I can imagine. Of course there are about a million more elegant ways to do what you want but it goes out of this answer's scope. I strongly recommend you to watch some programming tutorials or even better read a book.