Java constructor called multiple times?

Question

I built a program in order to test Java inheritance, there are several classes:

public class Animal {
    String name = "";
    String kind = "";

    public Animal() {
        System.out.println(desc());
    }

    public Animal(String name) {
        this.name = name;
        System.out.println(desc());
    }


    String desc() {
        if (name == "") {
            return "Je suis un animal.";
        } else {
            return "Je suis un animal de nom " + name + ".";
        }
    }
}




public class Mamifere extends Animal {    
    public Mamifere() {
        System.out.println(desc());
    }

    public Mamifere(String name) {
        this.name = name;
        System.out.println(desc());
    }

    String desc() {
        return super.desc() + " Je suis un mamifère.";
    }    
}

public class Homme extends Mamifere {    
    public Homme() {
        System.out.println(desc());
    }

    public Homme(String name) {
        this.name = name;
        System.out.println(desc());
    }

    String desc() {
        return super.desc() + " Je suis un homme.";
    }    
}

public class Chien extends Mamifere {    
    public Chien() {
        System.out.println(desc());
    }

    public Chien(String name) {
        this.name = name;
        System.out.println(desc());
    }

    String desc() {
        return super.desc() + " Je suis un chien.";
    }    
}

When I run this code:

public class TestAnimal {

    public static void main(String[] args) {
        Animal[] animaux = new Animal[5];
        animaux[0] = new Animal("Truc");
        animaux[1] = new Animal();
        animaux[2] = new Chien("Medor");
        animaux[3] = new Homme();
        animaux[4] = new Homme("Robert");

    }

}

I get this output:

Je suis un animal de nom Truc.
Je suis un animal.
Je suis un animal. Je suis un mamifère. Je suis un chien.
Je suis un animal. Je suis un mamifère. Je suis un chien.
Je suis un animal de nom Medor. Je suis un mamifère. Je suis un chien.
Je suis un animal. Je suis un mamifère. Je suis un homme.
Je suis un animal. Je suis un mamifère. Je suis un homme.
Je suis un animal. Je suis un mamifère. Je suis un homme.
Je suis un animal. Je suis un mamifère. Je suis un homme.
Je suis un animal. Je suis un mamifère. Je suis un homme.
Je suis un animal de nom Robert. Je suis un mamifère. Je suis un homme.

Why is there so many repetitions for the objects constructed from the argument less constructor ?

You seem to have defined `Homme` twice and omitted `Animal` from your question. Please correct this — Phil, Oct 21 '18 at 22:58
You have 2 levels of inheritance and are including super prints everywhere along with regular printing statements — faris, Oct 21 '18 at 23:02
See also [How do I compare strings in Java?](https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — shmosel, Oct 21 '18 at 23:20
It's also usually preferable to use `null` to indicate "unset", which is different from "a value that is empty". — chrylis -cautiouslyoptimistic-, Oct 22 '18 at 01:30
@chrylis Thank you! In this case though I am doing a recursive call where I need my string objects to have an actual empty value in order to recursively concatenate them. — Pop Flamingo, Oct 23 '18 at 18:58

azro · Accepted Answer · 2018-10-21T23:04:08.750

1

As Chien extends Mammifere and Mamifere extends Animal : when you want to instanciate an Chien it also builds an Mamifere as it's a super-type and so it also builds an Animal as it's also a super type

you're seeing the desc method launched by Chien constructor
you're seeing the desc method launched by Mamifere constructor
you're seeing the desc method launched by Animal constructor

The same happens hor Homme

edited Oct 21 '18 at 23:04

answered Oct 21 '18 at 23:01

azro

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That's interesting. Why does some IDEs (such as Eclipse), generate constructors where an explicit call (`super(args)`) to the superclass constructor is done ? Is there any difference with not calling it ? – Pop Flamingo Oct 21 '18 at 23:09
1

@TrevörAnneDenise when you need to call super-constructor with parameter it's required to use super(arg1, arg2, ..) but for no-param it's good practice bu it' would work without – azro Oct 21 '18 at 23:22
@TrevörAnneDenise as String are object, this is not a suprising behavior ;) – azro Oct 21 '18 at 23:32

Java constructor called multiple times?

1 Answers1