java default constructor issue

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I was looking over some code and voila:

C#

public class Classe {
    private String nomClasse;
    private Eleve[] enfants;
    private int nrEnfants = 0;
    private String[] matieres;
    private int nrMatieres = 0;

    public Classe(String nomClasse) {
        this.nomClasse = nomClasse;
        enfants = new Eleve[30];
        matieres = new String[10];
    }
}

and this being the only constructor for class ELEVE:

C#

public Eleve(String prenom, String nom) {
        this.nom = nom;
        this.prenom = prenom;
        notes = new Note[200];
    }

How on earth does this work? It instantiates the enfants array with 30 objects (null values). Is there still a default constructor?

Classe sixiemeA = new Classe("6eme A");

Posted 25-Aug-11 4:27am

samson radu

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Shameel · Answer 1 · 2011-08-25T05:11:00

Solution 1

The line:

Java

enfants = new Eleve[30];

only initializes the array. It does not initialize the objects within the array. You have to do it yourself by iterating the array instantiating each element of the array.

Java

for (Eleve e : enfants) {
      //Instantiate e here.
}

Posted 25-Aug-11 5:11am

Shameel

Updated 25-Aug-11 5:12am

v2

Comments

Manfred Rudolf Bihy 25-Aug-11 17:22pm

Proposed as the solution! 5+

Sergey Alexandrovich Kryukov 25-Aug-11 23:30pm

Agree, a 5.
--SA

fesben · Answer 2 · 2011-08-25T10:24:00

When you specify a new constructor then you lose the default constructor that you originally had. The only way to get a default constructor back is to make a new one that takes no parameters. Eg

Java

public Classe(){
   // define some code in here to initialize the variables that you've created
   enfants = new Eleve[30];
   // you can also go on to add things to the array after this like shameel said
   // you can use a loop or assign to the positions directly Eg
   enfants[0] = new Eleve("enfant1","1");
   // or using a loop to add values to the empty array :
   for(int i = 0; i < enfants.length; i++)
   {
      // this will go through the array and add a new instance of Eleve at each
      // level.
      enfants[i] = new Eleve("enfant" + i.ToString(), i.ToString());
   }
}

hope this helps.