Java constructor/object

Could someone help me figure out why is the print out = 0.0? Thanks

Code :

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public class AnnualFuelUse
{
    //Variables
    private int  distanceDay;
    private double amountAYear , distanceAnnual ;
 
    //Constructor
    AnnualFuelUse(int distance20Day, double timePerYear)
    {
        distanceDay = distance20Day;
        amountAYear = timePerYear;
        distanceAnnual= 0.00 ;
    }
 
    //Distance annual projection
    public void annualDis()
    {
    distanceAnnual = (distanceDay + amountAYear);
    }
    //Return distance annual
    public double getAnnualDis()
    {
        return distanceAnnual;
    }
}

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Code :

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public class AnnualFuelUseTester
{
    public static void main(String[]args)
    {
     AnnualFuelUse annualProject = new AnnualFuelUse(1110,18.25);
 
     System.out.println(annualProject.getAnnualDis());
}
}

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So, what did you expect or intend it to print?

I notice that getAnnualDis() - the thing that is printed - returns distanceAnnual and that there are exactly two places where this variable is given a value: the constructor and the annualDis() method. Use System.out.println() to see when or if the value of distanceAnnual changes.

Code :

---

public class AnnualFuelUse
{
    //Variables
    private int  distanceDay;
    private double amountAYear , distanceAnnual ;
 
    //Constructor
    AnnualFuelUse(int distance20Day, double timePerYear)
    {
        distanceDay = distance20Day;
        amountAYear = timePerYear;
        System.out.println("Constructor setting distanceAnnual to 0.0");
        distanceAnnual= 0.00 ;
    }
 
    //Distance annual projection
    public void annualDis()
    {
        System.out.println("annualDis setting distanceAnnual to " + (distanceDay + amountAYear));
        distanceAnnual = (distanceDay + amountAYear);
    }
    //Return distance annual
    public double getAnnualDis()
    {
        return distanceAnnual;
    }
}

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What variable's value is being printed? Where does that variable get assigned a value?
Is the code that assigns the variable a value executed before its value is printed?

@pbrockway2, wouldn't the value of distanceAnnual change to what ever (distanceDay + amountAYear) is and then return that value? Could you explain why it return 0 ? Also, how can I make it display System.out.println("annualDis setting distanceAnnual to " + (distanceDay + amountAYear)); ? Thanks

** Is it because I haven't invoke the annualDis method?

--- Update ---

Quote:

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Originally Posted by Norm

What variable's value is being printed? Where does that variable get assigned a value?
Is the code that assigns the variable a value executed before its value is printed?

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The variable value that I'm trying to print is distanceAnnual in the getAnnualDis() method. This variable get assigned 0.00 in the constructor then it is assign the value of distanceDay + amountAYeear in the AnnualDis() method. - I think I haven't invoke the method where distanceAnnual is assigned a new value that is why.

--- Update ---

I got it now. Thanks you so much!

Quote:

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haven't invoke the method where distanceAnnual is assigned a new value

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You need to call that method to have some value put into the variable before printing it.

Quote:

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wouldn't the value of distanceAnnual change to what ever (distanceDay + amountAYear) is and then return that value?

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It isn't a question of "wouldn't...?", it's a question of "does it ... or not?". In other words the task at this point is to see what is going on. The code I posted - which is just yours with a couple of lines added - should answer this question. Just add those two lines, compile and run.

At that point you should be able to answer Norm's three questions.

Quote:

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Could you explain why it return 0 ?

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Well, it returns zero because that's the value of distanceAnnual. Run the (ammended) code to see why. Or, if it's still not clear, describe what it does output.

[Edit] Massively slow :( Well done! Yes, you have to call a method for it to do its work.