Can objects inherit string representations?

Question

I have the following problem with displaying an object as a string:

class Gast{

    String voorNaam, achterNaam;
    datum geboorteDatum;

    Gast(String vNaam, String aNaam, datum input){

        voorNaam = vNaam;
        achterNaam = aNaam;
        geboorteDatum = input;
    }

    public String toString(){

        return("Naam: " + voorNaam + " " + achterNaam + " " + geboorteDatum);
    }
}

here I implemented a way to represent this object in a string, however when I try to use that in this class:

class Kamer{

    boolean vrij;
    Gast gast;

    Kamer(){}

    public String toString(){

         if(vrij == true){

             return "De kamer is vrij!";
         }

         else{

             return gast;
         }
    }
}

I get the following error:

kamer.java:17: error: incompatible types: Gast cannot be converted to String
        return gast;

I gave a string representation of the object Gast in its class? Does the other class not inherit the representation I gave?

Because Gast is not a string. You have to call gast.toString(). — markspace
– markspace, Commented Nov 6, 2015 at 20:41
Thank you that fixed the error! and made me feel a bit stupid haha. Should i keep the question? — Arkin Zoodsma
– Arkin Zoodsma, Commented Nov 6, 2015 at 20:44
"Should i keep the question?" you have no choice since it has up-voted answer... — Pshemo
– Pshemo, Commented Nov 6, 2015 at 20:45
as you maybe realized i am pretty new on stack overflow community but thank you for the help! — Arkin Zoodsma
– Arkin Zoodsma, Commented Nov 6, 2015 at 20:50

kcraigie · Accepted Answer · 2015-11-06 21:12:49Z

7

Try:

return gast.toString();

Edit: Better yet, as suggested by @Andreas comment, use String.valueOf(gast) if there is a possibility gast can be null (or just check for null manually)

edited Nov 6, 2015 at 21:12

answered Nov 6, 2015 at 20:42

kcraigie

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3 Comments

Andreas Over a year ago

Oh no, please no. Don't use "" + gast. If gast can be null, use String.valueOf(gast), not that bad construct, which compiles to new StringBuilder().append(gast).toString(). <shivers>

Andreas Over a year ago

Followup: "" + gast results in: allocate StringBuilder, allocate char[16], allocate char[?] for actual length, copy text, allocate String, allocate char[?], copy text. 4-5 allocations and 2 copies of the text for each execution. All that overhead at runtime, just to save a few keystrokes. Sorry, pet peeve of mine.

kcraigie Over a year ago

@Andreas ok ok, i'll get rid of it :)

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