compareTo

[Kenneth Van Gysegem]

hi,
I have a question,
I'm making a class employer where there are 3 properties:
1) int day;
2)int month;
3)int year;

Now the problem is i want to compare the inputted dates.
My class implements Comparable, I have already written the equals()-method.
But now I am stuck on the compareTo- method...
I want it to rank the date lower if the the dates are equal or lower, and higher if there higher.

I added my code, it's written in dutch though, so I hope it doesn't make things too difficult.
the WerknemersDatum is my own class with the 3 properties and there setters and getters.

Thanks in advance,
Kenneth.
PS as you can see I tried but misarably failed.

package be.vdab.personeel;

import be.vdab.util.Datum;
import be.vdab.util.WerknemersDatum;


//Nog te doen: CompareTo met datumInDienst 




    
   
   
public abstract class Werknemer implements Comparable<Werknemer> {
   private int personeelsNummer=-1;
   private WerknemersDatum datumInDienst; //nog veranderen naar eigen type WerknemersDatum
   private String naam="Nog niet ingevuld";
   
   public Werknemer(){}
   public Werknemer(int personeelsNummer, WerknemersDatum datumInDienst, String naam){
       setDatumInDienst(datumInDienst);
       setNaam(naam);
       setPersoneelsNummer(personeelsNummer);
   }
   
    public abstract double getVerloning();
    public int getPersoneelsNummer() {
        return personeelsNummer;
    }
    public void setPersoneelsNummer(int personeelsNummer) {
        if (personeelsNummer>0)
        this.personeelsNummer = personeelsNummer;
    }
    public String getNaam() {
        return naam;
    }
    public void setNaam(String naam) {
        this.naam = naam;
    }
    public WerknemersDatum getDatumInDienst() {
        return datumInDienst;
    }
    public void setDatumInDienst(WerknemersDatum datumInDienst) {
        this.datumInDienst = datumInDienst;
    }
    //eerst equals uitschrijven om zo de compareTo te gebruiken
    @Override
    public boolean equals(Object o){
        if (o==null){
            return false;
        }
        else if(o instanceof Werknemer)
            { //test of o een Werknemer-object is
             Werknemer w = (Werknemer)o; //cast o naar Werknemer en stel gelijk aan w
             if (datumInDienst == w.getDatumInDienst())
                    return true;
             else return false;
            }
         else return false;
        }

    @Override
    public int compareTo(Werknemer o) {
        if(this.equals(o)){
            return 0;
        }
        else 
            if (this.datumInDienst<=o.getDatumInDienst())return -1;
        
//            if (this.datumInDienst.getJaar()>o.getDatumInDienst().getJaar()){
//                return 1;
//            }
//            else if (this.datumInDienst.getJaar()<o.getDatumInDienst().getJaar()){
//                return -1;}
//            
//             else 
//                if(this.datumInDienst.getJaar()==o.getDatumInDienst().getJaar()){
//                        if (this.datumInDienst.getMaand()<o.getDatumInDienst().getMaand()){
//                        return -1;
//                        }
//                        else if (this.datumInDienst.getMaand()>o.getDatumInDienst().getMaand()){
//                        return 1;
//                        }
//                        else if (this.datumInDienst.getDag()<=o.getDatumInDienst().getDag()){
//                            return -1;
//                        } 
//                        if (this.datumInDienst.getDag()>o.getDatumInDienst().getDag()){
//                            return 1;
//                        }
//                } 
    
        }//end compareTo
    @Override
    public String toString(){
        return personeelsNummer +"; "+datumInDienst+"; "+naam;
    }
}//end class werknemer

[Jesper de Jong]

Kenneth Van Gysegem wrote:I added my code, it's written in dutch though, so I hope it doesn't make things too difficult.

Not at all (for me atleast... )

Kenneth Van Gysegem wrote:PS as you can see I tried but misarably failed.

Why; what is wrong with the code you wrote and commented out? The logic seems correct, at first sight, except line 69, that should be removed.

[Kenneth Van Gysegem]

OK,
yeah line 69 was a sort of trie afterwards, luckily i didn't erase all the other code. hehe

The thing is the compareTo gets an errormessage: "returnstatement missing", but I don't see where.
Also isn't this a diffuclt way to do this?

thanks,
Kenneth

PS ben je van Belgie of Nederland?
alleszins aangenaam

[Matthew Brown]

Kenneth Van Gysegem wrote:The thing is the compareTo gets an errormessage: "returnstatement missing", but I don't see where.

The line if(this.datumInDienst.getJaar()==o.getDatumInDienst().getJaar()) (line 78) doesn't have a corresponding else clause. So if it hits that line and the condition is false there's no return value specified.

I'm pretty sure you can simplify it a bit, though. Have a look at java.lang.Integer#compare(int,int), which already does what is needed for a single integer. Use that on the year. If it's non-zero, just return it. Otherwise continue to the month, etc. So you only need two if statements with that.

There's also a slightly cheaty version that relies on you knowing (and enforcing) an upper limit for day and month. Just compare day + 32*(month + 13*year)).

[Kenneth Van Gysegem]

Thanks Matthew,

In the end I didn't do it your way but you helped me a lot with the line 78 tip!
Don't know how i could've missed it.

In the end I did it this way

 @Override
    public int compareTo(Werknemer o) {
        if(this.equals(o)){
            return 0;
        }
else 
                    if(this.datumInDienst.getJaar()==o.getDatumInDienst().getJaar()){
                        if (this.datumInDienst.getMaand()<o.getDatumInDienst().getMaand()){
                        return -1;
                        }
                        else if (this.datumInDienst.getMaand()>o.getDatumInDienst().getMaand()){
                        return 1;
                        }
                        else if (this.datumInDienst.getDag()<=o.getDatumInDienst().getDag()){
                            return -1;
                        } 
                        if (this.datumInDienst.getDag()>o.getDatumInDienst().getDag()){
                            return 1;
                        }
                    } 
                if (this.datumInDienst.getJaar()<o.getDatumInDienst().getJaar()){
                    return -1;
                }
                else return 1;
        }//end compareTo

I will however bear your advice in mind, and study the subject a little more.
Thanks again,
Kenneth

[Ivan Jozsef Balazs]

if (this.datumInDienst<=o.getDatumInDienst())return -1;  

However datumInDienst is of the type WerknemersDatum.

Anyway.

If the compiler does not deduce (can not be sure) a value is returned on every execution path from a non-void method, it will complain.

For example this won't compile either:

int foo (boolean boo) {

if (boo) return -1;

if (!boo) return 1;

}