Command Line and Array in Java

Question

I'm learning using an Array and Command line argument for Java. We write a program that convert from Celsius degree to Fahrenheit degree. I started a basic idea for my project but not sure I did it right (I'm beginner).

public class Implementation 
{
    public static void main(String[] args)
    {
        {
        String[] days = new String[7];
        days[0] = "Very Cold";
        days[1] = "Cold";
        days[2] = "Mild";
        days[3] = "Very Mild";
        days[4] = "Warm";
        days[5] = "Very Warm";
        days[6] = "Hot";
        }
        if (args.length != 5)
        {
            System.out.println("Error! Please try again.");
            System.exit(0);
        }
        else
        {
            String name;
            String convert;
            double degree;
            String celsius;
            String fahrenheit;

            name = args[0];
            convert = args[1];
            degree = Double.parseDouble(args[2]);
            celsius = args[3]; 
            fahrenheit = args[4];         

            System.out.printf("%n%s Celsius is %.2f Fahrenheit\n", args[2], ( 9.0 / 5.0 *  (degree + 32)));
        }
    }
}

When I supply my command line argument, it should be in this form:
Java TempConversion 100 c f

My questions are: Did I do my command line arguments right? It seem like I did something wrong even though I still have the same output. How do I show up my array in the output with specific degree? Follow this:

Below 0 degrees = Very cold

From 0 to 32 = Cold

From 33 to 50 = Mild

From 51 to 60 = Very mild

From 61 to 70 = Warm

From 71 to 90 = Very warm

Above 90 = Hot

Answer 1

A couple of things:

• "Java" and the program name (TempConversion) aren't arguments. Everything after that is. So when you put args.length != 5 you weren't counting the program name and the java keyword. You should use args.length != 3 (as opposed to 5).

  • e.g. The arguments (in the example) are {"100", "c", "f"} with the assignments 0, 1, 2.

Edit:

A question was asked as to how to get the program name and java keyword.

• The java keyword is a constant. That is you can use "Java" for all programs.

• To find the class name you can see this post. Here is my implementation. Should work.

• This likely won't cause you much grief, but I don't see a reason for those brackets starting around String[] days and ending at day[6] =...; " }". There isn't a need for them and String[] can have elements that are set and used anywhere (No braces required). Everything else looks fine.

Answer 2

In java TempConversion 100 c f your command line arguments are 100 and c and f -- there are three arguments, but you are checking for five arguments in if (args.length != 5) This is unlike C where argv[0] is the program name itself.

You can see this with a minimal program

public class c2f
{
    public static void main(String[] args)
    {
        System.out.println("args.length is " + args.length);

        for (int i=0; i<args.length; i++) {
            System.out.println("arg[" + i + "] is " + args[i]);
        }
    }
}

Run this as

javac c2f.java
java c2f 100 c f

Your output should be

args.length is 3
arg[0] is 100
arg[1] is c
arg[2] is f

You are also not looking at either the "c" or the "f" arguments. Maybe you intend to add to your program so those tell you if you want to do a C->F or a F->C conversion.