Overloading constructor question

Question

The following douse not seem to work:-
class A {
     A( int i ) {
          System.out.println( "A constructor" + i );
class B {
     B( int i ) {
          System.out.println( "B constructor" + i );
class C extends A {
     C () { // line 17
          System.out.println( "C constructor" );
     public static void main( String[] args ) {
          C c = new C();
It complaines at line 17
A(int) in A cannot be applied to ()
C () {
^
This has totaly bafeld be. I thought it was OK to add overloaded constructors in inheratid classes but it seems to be complaining that I am replacing C(int) wit C(), i.e. the constructor in the subclass has diferent arguments. surly this should simply add an overloaded constructer?
Ben

Answer 1

The first statement in every constructor must be a call to either a) another constructor in that class or b) a constructor of the super class. If you do not specify a call to either, then the compiler automatically will insert a call to the no argument constructor of the super class. Since there isn't a no-arg constructor in A, the compiler complains that you are calling the A(int) constructor with no arguments. You need to either add a no argument constructor to A, or you need to call the A(int) constructor from the C constructor with some default value.
In case you didn't know, to call a super constructor from a subclass, you use the super keyword.
Example:
class A {
    A(int i) {}
class B extends A {
    B() {
        super(2);  //This call the A(int) constructor.
}