Java默认构造函数问题 [英] java default constructor issue

问题描述

我正在查看一些代码，瞧:

I was looking over some code and voila:

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];
    }
}

这是ELEVE类的唯一构造函数:

and this being the only constructor for class ELEVE:

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

这到底如何工作?它使用30个对象(空值)实例化enfants数组.还有默认的构造函数吗?

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

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");

推荐答案

该行:

enfants = new Eleve[30];

仅初始化数组.它不会初始化数组内的对象.您必须自己通过实例化数组的每个实例来迭代数组.

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.

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

指定新的构造函数后，您将失去最初拥有的默认构造函数.恢复默认构造函数的唯一方法是制作一个不带参数的新构造函数.例如

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

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());
   }
}

希望对您有所帮助.

hope this helps.

这篇关于Java默认构造函数问题的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！