=?iso-8859-1?Q?Re:_=5Bjava-list=5D_Heran=E7a_de_construtores?=

Thu, 01 Nov 2001 16:53:31 -0800

O Contructor nao eh herdado, mas o construtor da classe filha chama o default constructor (o sem parametros) da classe mae automaticamente, exceto se voce explicitamente chamar um outro construtor na class mae.
 
Outra coisa que vc deve notar eh que se voce nao criar nenhum construtor para a sua classe, o compilador cria o default constructor para voce.
 
Abracos,
Marcelo Quintella
----- Original Message -----
From: Airton
Sent: Thursday, November 01, 2001 1:09 PM
Subject: [java-list] Heran�a de construtores

Ol�.

Entendi pelo trecho abaixo do The Java Tutorial, que construtores n�o podem ser herdados:

What Members Does a Subclass Inherit?

Rule:  A subclass inherits all of the members in its superclass that are accessible to that subclass unless the subclass explicitly hides a member variable or overrides a method. Note that constructors are not members and are not inherited by subclasses.
 
 
 
O trecho a seguir faz parte do cap�tulo 6 do livro Thinking in Jana, 2nd edition, Revision 12 de Bruce Eckel, mostrando que os construtores s�o herdados das classes bases, at� mesmo se vc n�o criar um (ver �ltima linha do trecho):
 
 
Java automatically inserts calls to the base-class constructor in the derived-class constructor. The following example shows this working with three levels of inheritance:
//: c06:Cartoon.java
// Constructor calls during inheritance.

class Art {
  Art() {
    System.out.println("Art constructor");
  }
}

class Drawing extends Art {
  Drawing() {
    System.out.println("Drawing constructor");
  }
}

public class Cartoon extends Drawing {
  Cartoon() {
    System.out.println("Cartoon constructor");
  }
  public static void main(String[] args) {
    Cartoon x = new Cartoon();
  }
} ///:~

The output for this program shows the automatic calls:

Art constructor
Drawing constructor
Cartoon constructor

You can see that the construction happens from the base �outward,� so the base class is initialized before the derived-class constructors can access it. [ Add Comment ]

Even if you don�t create a constructor for Cartoon( ), the compiler will synthesize a default constructor for you that calls the base class constructor. [ Add Comment ]

 

O que entendi errado? � interessante colocar os membros da super classe a ser herdada nos construtores ou � melhor evitar? Por qu�?

Obrigado,

Airton

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