[java] Is Constructor Overriding Possible?

What i know is, the compiler writes a default no argument constructor in the byte code. But if we write it ourselves, that constructor is called automatically. Is this phenomena a constructor overriding?

While others have pointed out it is not possible to override constructors syntactically, I would like to also point out, it would be conceptually bad to do so. Say the superclass is a dog object, and the subclass is a Husky object. The dog object has properties such as "4 legs", "sharp nose", if "override" means erasing dog and replacing it with Husky then Husky would be missing these properties and be a broken object. Husky never had those properties and simply inherited them from dog. On the other hand, if you intend to give Husky everything that dog has, then conceptually you could "override" dog with Husky, but there would be no point in creating a class that is the same as dog, it's not practically an inherited class but a complete replacement.

Constructor looks like a method but name should be as class name and no return value.

Overriding means what we have declared in Super class, that exactly we have to declare in Sub class it is called Overriding. Super class name and Sub class names are different.

If you trying to write Super class Constructor in Sub class, then Sub class will treat that as a method not constructor because name should not match with Sub class name. And it will give an compilation error that methods does not have return value. So we should declare as void, then only it will compile.

Cannot override constructor. Constructor can be regarded as static, subclass cannot override its super constructor.

Of course, you could call protected-method in super class constructor, then overide it in subclass to change super class constructor. However, many persons suggest not to use the trick, in order to protect super class constructor behavior. For instance, FindBugs will warn you that a constructor calls a non-final method.

method overriding in java is used to improve the recent code performance written previously .

some code like shows that here we are creating reference of base class and creating phyisical instance of the derived class. in constructors overloading is possible.

InputStream fis=new FileInputStream("a.txt");
int size=fis.available();

size will return the total number of bytes possible in a.txt so

Constructors are not normal methods and they cannot be "overridden". Saying that a constructor can be overridden would imply that a superclass constructor would be visible and could be called to create an instance of a subclass. This isn't true... a subclass doesn't have any constructors by default (except a no-arg constructor if the class it extends has one). It has to explicitly declare any other constructors, and those constructors belong to it and not to its superclass, even if they take the same parameters that the superclass constructors take.

The stuff you mention about default no arg constructors is just an aspect of how constructors work and has nothing to do with overriding.

It should also be noted that you can't override the constructor in the subclass with the constructor of the superclass's name. The rule of OOPS tells that a constructor should have name as its class name. If we try to override the superclass constructor it will be seen as an unknown method without a return type.

You can have many constructors as long as they take in different parameters. But the compiler putting a default constructor in is not called "constructor overriding".

Because a constructor cannot be inherited in Java and Method Overriding requires inheritance. Therefore, it's not applicable.

No it is not possible to override a constructor. If we try to do this then compiler error will come. And it is never possible in Java. Lets see the example. It will ask please write a return type o the method. means it will treat that overriden constructor as a method not as a constructor.

package com.sample.test;

class Animal{

    public static void showMessage()
    {
        System.out.println("we are in Animal class");
    }
}

class Dog extends Animal{

    public void DogShow() 
    {
        System.out.println("we are in Dog show class");
    } 

    public static void showMessage()
    {
        System.out.println("we are in overriddn method of dog class");
    }
}

public class AnimalTest { 

    public static void main(String [] args)
    {
        Animal animal = new Animal();
        animal.showMessage();

        Dog dog = new Dog();
        dog.DogShow();

        Animal animal2 = new Dog();
        animal2.showMessage();
    }

}

Constructor overriding is not possible because of following reason.

Constructor name must be the same name of class name. In Inheritance practice you need to create two classes with different names hence two constructors must have different names. So constructor overriding is not possible and that thought not even make sense.

But if we write it ourselves, that constructor is called automatically.

That's not correct. The no-args constructor is called if you call it, and regardless of whether or not you wrote it yourself. It is also called automatically if you don't code an explicit super(...) call in a derived class.

None of this constitutes constructor overriding. There is no such thing in Java. There is constructor overloading, i.e. providing different argument sets.

I found this as a good example for this question:

    class Publication {

    private String title;

    public Publication(String title) {
        this.title = title;
    }

    public String getDetails() {
        return "title=\"" + title + "\"";
    }

}

class Newspaper extends Publication {

    private String source;

    public Newspaper(String title, String source) {
        super(title);
        this.source = source;
    }

    @Override
    public String getDetails() {
        return super.getDetails() + ", source=\"" + source + "\"";
    }
}

class Article extends Publication {

    private String author;

    public Article(String title, String author) {
        super(title);
        this.author = author;
    }

    @Override
    public String getDetails() {
        return super.getDetails() + ", author=\"" + author + "\"";
    }

}

class Announcement extends Publication {

    private int daysToExpire;

    public Announcement(String title, int daysToExpire) {
        super(title);
        this.daysToExpire = daysToExpire;
    }

    @Override
    public String getDetails() {
        return super.getDetails() + ", daysToExpire=" + daysToExpire;
    }

}

It is never possible. Constructor Overriding is never possible in Java.

This is because,

Constructor looks like a method but name should be as class name and no return value.

Overriding means what we have declared in Super class, that exactly we have to declare in Sub class it is called Overriding. Super class name and Sub class names are different.

If you trying to write Super class Constructor in Sub class, then Sub class will treat that as a method not constructor because name should not match with Sub class name. And it will give an compilation error that methods does not have return value. So we should declare as void, then only it will compile.

Have a look at the following code :

Class One
        {
         ....
         One() { // Super Class constructor
          .... 
        }

        One(int a) { // Super Class Constructor Overloading
          .... 
        }
 }

Class Two extends One
                   {
                    One() {    // this is a method not constructor 
                    .....      // because name should not match with Class name
                   }

                    Two() { // sub class constructor
                   ....  
                   }

                   Two(int b) { // sub class constructor overloading
                   ....
                  }
 }  

Your example is not an override. Overrides technically occur in a subclass, but in this example the contructor method is replaced in the original class.