Converting Units using if statements?

Question

I have to write a program to convert between linear units in, ft, mi, mm, cm, m, km. I know there are easier and better ways to do this. I think we'ere just trying to fully understand if else if statements. But this is what I have so far. I'm just trying to figure out if I am on the right track. I've tried to write out some pseudocode but it just seems like a lot going on so I find it a bit overwhelming. Next I'm going to add a method to convert form in or mm to whatever is selected by the user.

When I test the program i get this: UnitConversion@76c5a2f7 (EDIT: THIS ISSUE WAS FIXED) Ok I made the suggested changes and that allowed the first part of the program to run properly. I have now added my second method to convert from in/mm to the other measurements.. I was having issues but I figured it out.

Here is my main method;

public class LinearConversion 
{
    public static void main(String[] args)
    {
        UnitConversion newConvert = new UnitConversion("km", "m", 100);

        System.out.println(newConvert);
    }
}

Any suggestions? What am I missing or not understanding about doing this sort of program?

    public class UnitConversion 
{

    private String input;
    private String output;
    private double value;
    private double temp;

    private double in, ft, mi, mm, cm, m, km;
    private final double inch_feet = 12;
    private final double inch_miles = 63360;


    private final double inch_millimeters = 25.4;
    private final double inch_centimeters = 2.54;
    private final double inch_meters = 0.0254;
    private final double inch_kilometers = 0.0000254;

    private final double millimeters_inch = 0.0393701;
    private final double millimeters_feet = 0.00328084;
    private final double millimeters_miles = 0.000000622;

    private final double millimeter_centimeters = 10;
    private final double millimeter_meters = 1000;
    private final double millimeter_kilometers = 1000000;

    public UnitConversion(String in, String out, double val)
    {
        input = in;
        output = out;
        value = val;
    }

    public String toString()
    {
        if (input.equals("mi"))
        {
            in = value * inch_miles; 
            input = "in";
        }

        else if (input.equals("ft"))
        {
            in = value * inch_feet;
            input = "in";
        }

        else
        {
            in = value;
            input = "in";
        }

        if (input.equals("km"))
        {
            mm = value * millimeter_kilometers;
            input = "mm";
        }

        else if (input.equals("m"))
        {
            mm = value * millimeter_meters;
            input = "mm";
        }

        else if (input.equals("cm"))
        {
            mm = value * millimeter_centimeters;
            input = "mm";
        }

        else
        {
            mm = value;
            input = "mm";
        }

        return value + input + " " + output;
    }

     public double getUnit()
    {
        if (input.equals("in"))
        {
            if (output.equals("ft"))
            {
                ft = in * inch_feet;
                System.out.println(ft + "ft");
            }
            else if (output.equals("mi"))
            {
                mi = in * inch_miles;
                System.out.println(mi + "mi");
            }
            else if (output.equals("mm"))
            {
                mm = in * inch_millimeters;
                System.out.println(mm + "mm");
            }
            else if (output.equals("cm"))
            {
                cm = in * inch_centimeters;
                System.out.println(cm + "cm");
            }
            else if (output.equals("m"))
            {
                m = in * inch_meters;
                System.out.println(m + "m");
            }
            else if (output.equals("km"))
            {
                km = in * inch_kilometers;
                System.out.println(km + "km");
            }  
            else 
            {
                System.out.println(in + "in");
            }  
        }
        else
        {
            if (output.equals("cm"))
            {
                cm = mm * millimeter_centimeters;
                System.out.println(cm + "cm");
            }
            else if (output.equals("m"))
            {
                m = mm * millimeter_meters;
                System.out.println(m + "m");
            }
            else if (output.equals("km"))
            {
                km = mm * millimeter_kilometers;
                System.out.println(km + "km");
            }
            else if (output.equals("in"))
            {
                in = mm * millimeters_inch;
                System.out.println(in + "in");
            }
            else if (output.equals("ft"))
            {
                ft = mm * millimeters_feet;
                System.out.println(ft + "ft");
            }
            else if (output.equals("mi"))
            {
                mi = mm * millimeters_miles;
                System.out.println(mi + "mi");
            }
            else 
            {
                System.out.println(mm + "mm");
            }
        }
}

Answer 1

Basically, you need/want to give a String argument to System.out.println in order to display it.

Thus, when you use System.out.println with an Object (that is not a String) as the argument, Java actually outputs the result of the toString method on that object.

If you haven't overridden it, the Object class' implementation of toString is used: this is what gives you your current output: UnitConversion@76c5a2f7.

To learn more about how is this default toString implementation generating that String, you can refer to the javadoc entry for Object#toString.

Answer 2

Base on your output, and your provided code, yes! Rename String getInput() to String toString() and your current main() will work, or change your current main()

System.out.println(newConvert.getInput()); // <-- added .getInput()