Two classes issue

Question

I have asked you about GregorianCalendar and Calendar and some people said that Calendar is better. So I did it with Calender class.

I have a problem with one method: JavaApplication1#whichIsEarlier(), always receives error. Please check it, if you can. How to resolve it? I'll appreciate your help.

 public class JavaApplication1 {


public static void main(String[] args) {
    Calendar yy =Calendar.getInstance();
    Calendar xx= Calendar.getInstance();
    xx.set(2001, 10,10);
    Data dt = new Data(yy);
    Data xt = new Data(xx);
    Data dd = new Data( yy, xx);
    System.out.println(dt.toString());
    System.out.println(xt.toString());       
    System.out.println(dd.whichIsEarlier());
}
}


class Data {
    private Calendar calendar;
     Calendar cale;
    Data(Calendar x){

    calendar = x;
}

Data(Calendar x, Calendar y){
    calendar = x;
    cale = y;
}

public String toString(){ 
    String months[] = {"Jan","Feb", "Mar" , "Apr", "Mai", "June", "July","Aug",
        "Sep", "Okt", "Nov", "Dec"};
    String str = "";
    str = "Data: "+ calendar.get(Calendar.DATE) +" "+ months[calendar.get(Calendar.MONTH)]+
        " "+ calendar.get(Calendar.YEAR);
        return str;

    }

    public String whichIsEarlier(Calendar cale){
        String str = "";
        if(calendar.after(cale)) str = calendar.toString() ;
        else str = cale.toString();
        return str +" jest wczesniej";
    }
 }

First check the signature of the method `whichIsEarlier`, and then see if you are invoking it correctly? — Rohit Jain, Aug 24 '13 at 08:31
"Some people said that `Calendar` is better" - well `GregorianCalendar` is simply a subclass of `Calendar`. It's not a matter of one being "better" - it's a matter of choosing which to use based on the context. — Jon Skeet, Aug 24 '13 at 08:33
@JonSkeet Also, `Calendar` is abstract. It just so happens that `GregorianCalendar` is the only concrete subclass most people have ever seen, but otherwise all the usual interface/implementation issues apply. — chrylis -cautiouslyoptimistic-, Aug 24 '13 at 08:35
@hexafraction The error is obvious: `whichIsEarlier()` cannot be applied to `whichIsEarlier(Calendar)`. — Marko Topolnik, Aug 24 '13 at 08:39
@MarkoTopolnik And the compiler error message in such cases is quite clear. — chrylis -cautiouslyoptimistic-, Aug 24 '13 at 08:42
So, it's impossible to do it?Is method wichIsEalier made correct or not? — dzoni, Aug 24 '13 at 08:50

score 0 · Answer 1 · answered Aug 24 '13 at 08:50

0

System.out.println(dd.whichIsEarlier());

is problematic as you only define a Data#whichIsEarlier(Calender).

Please make sure that either the whichIsEarlier call passes in a calendar object, or you create a new whichIsEarlier that takes no arguments and has calendars predefined.

answered Aug 24 '13 at 08:50

nanofarad

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ok, so i have to do like that: System.out.println(dt.whichIsEalier(xx)); ? – dzoni Aug 24 '13 at 08:53
@dzoni Yes, so you call `Data#whichIsEarlier(Calendar)`. – nanofarad Aug 24 '13 at 09:01
Ok, thanks but next problem which was appeared is calendar.toString() inside whichIsEalier, it doesn't work :( – dzoni Aug 24 '13 at 09:05
@dzoni Then create your own implementation that accepts a `Calendar` and generates a string with its properties. – nanofarad Aug 24 '13 at 09:08

score 0 · Accepted Answer · answered Aug 24 '13 at 09:01

This is how I would clean up your code:

class Data {
  private Calendar calendar;

  Data(Calendar x) { calendar = x; }

  public String whichIsEarlier(Data other) {
    return (calendar.after(other.calendar)? this : other)
        + " jest wczesniej";
  }

(I have elided toString; I'm not getting into its issues for this answer).

Note:

removed the cale instance variable
removed the two-argument constructor;
whichIsEarlier accepts another Data, not another Calendar;
its return value doesn't call calendar.toString but rather your own object's toString
and it does it implicitly (string concatenation does that).

And now the main method should go like

public static void main(String[] args) {
  Calendar yy =Calendar.getInstance();
  Calendar xx= Calendar.getInstance();
  xx.set(2001, 10,10);
  Data dt = new Data(yy);
  Data xt = new Data(xx);
  System.out.println(dt.whichIsEarlier(xt));
}

I know that I can get a punishment for that, but thank you so much i was looking for it for a long time and I have noone who can explain it me. :)! — dzoni, Aug 24 '13 at 09:12
No punishment, people here just like to remind newcomers about accepting answers, which you already have :-) — Marko Topolnik, Aug 24 '13 at 09:19

Two classes issue

2 Answers2