Why does the child class need to implement the parent classes constructor?/

Question

As I was playing around with some code I came across this point :
First Class
public class A {
     public int x;
     A(int i){
          x=i;
          System.out.println("A is initialised");
}Second Class extending it :
public class B extends A{
     private int y;
   // Why do I need this constructor to call parents constructor?
  // My guess is so that when i make an object of class B referring to class A it should make sense?
     B(int i) {                     
          super(i); 
          y=test;
public static void main(String args[]){
      A a = new A(1);
      A b = new B(1); make an object of class B referring to class A it should work!!
      B c = new B(2);
      B d =(B) new A(2);  --> gives class cast exception!
}I am little confused here, Can someone throw more light on it.
Thanks

Answer 1

You don't override constructors. However, every class, in it's constructor, must call some constructor from the class it's extending. In most cases this is simply super(). However, if your class does not have a default constructor (i.e. you've declared any other constructor, or the sub class does not have access to it, I.E. you've declared it private) then you must include a call to some other constructor in the super class. The constructor in the subclass does not have to be the same as the super class one, but you do have to invoke a constructor from the super class. I.E.
class A {
  A(int i) {}
class B extends A {
  B(String b) {
    super(0);
}