what is the usage of super() to invoke super class constructor!

[krishnadhar Mellacheruvu]

Hi

class demo1
{

	demo1()
	{
		System.out.println("SuperClass Constructor!");
	}
}

class Superdemo extends demo1
 {
	
	Superdemo()
	{
		//super();
		System.out.println("ChildClass Constructor!");
	}
	 
	 
public static void main(String[] args) {

Superdemo sd = new Superdemo();
	


}

when the above program is executed first SuperClass Constructor and then ChildClass constructor is (executed)displayed. What is the use of having the super keyword in the child class constructor when infact the super class constructor is executed when the object for the child class is created since the child class extends to the superclass.

Thanks

[Stephan van Hulst]

There's no real use to call super(), because it's called implicitly whether you write it or not. Some people prefer to make it explicit, but it's unnecessary.

However, it *is* important to call super(...) at the start of the constructor if you want to invoke a superclass constructor that has parameters. Here's an example:

class Person {

  private final String name;

  Person(String name) {
    if (name == null)
      throw new IllegalArgumentException();

    this.name = name;
  }

  String name() {
    return name;
  }
}

class Employee extends Person {

  private final String id;

  Employee(String name, String id) {
    super(name);
    
    if (id == null)
      throw new IllegalArgumentException();

   this.id = id;
  }

  String id() {
    return id;
  }
}

[krishnadhar Mellacheruvu]

Thanks stephan,

So unless we have to call the constructor which has got parameters it's ok not to use super keyword as this is implicitly called.. correct me if am wrong...

[Stephan van Hulst]

Yes that's correct.

[Ganesh Patekar]

Let creation of an object of subclass invokes non-parameterized Or parameterized constructor of subclass, implicitly It invokes non-parameterized constructor of superclass by default. Sometime you may need to invoke a particular type of superclass's constructor rather than non-parameteried as given in Stephan's example then you can use super keyword.

That super keyword statement should always be first statement in constructor of subclass.