a bug with a constructor

[alex lotel]

i dont know what the problem here?

public class main_class {
 
/**
 * @param args
 */
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
B b=new B(7,11);
A a=((A)b).done();
System.in.read();
}
}
 

 
public class B extends A {
int a=1;
int b=2;
B(int a,int b)
{
this(a);
a=b;
}
B(int b){   ///here is my bug
a=b;
}
A done(){
System.out.println("iam finished");
return this;
}
public void print(int a,int b,int c){
System.out.println("a"+a);
System.out.println("b"+b);
System.out.println("c"+c);
}
}
 

public interface C {
void print (int a,int b,int c);
}
 

public abstract class A implements C {
public int d=17;
A(int d){
this.d=d;
}
A done (){
System.out.println("iam done");
return this;
}
 
}

[Joanne Neal]

Originally posted by donaldth smithts:
i dont know what the problem here?
[/CODE]

If you tell us the symptoms we may be able to diagnose it.

[Campbell Ritchie]

You are passing the value a to the 2nd constructor and giving it the title "a". Then you are giving "a" the value of b in the 1st constructor.

Does that help?

[alex lotel]

it says "implicit super constructor A() is undefined.Must explicitly invoke another constructor"

can you tell me whats the mistake in normal words?

[Joanne Neal]

If you don't include a call to any of the parent class constructors (using super) in your constructors, then the compiler implicitly includes a call to the parent classes no arg constructor. If the parent class doesn't have a no arg constructor then you get this error.

The solution is to either add a no arg constructor to your A class or explicitly include a call to one of the A class constructors in your B class constructors.
e.g.

B(int b) {   ///here is my bug
  super(b);
  a=b;
}

[Roger Chung-Wee]

Whenever a class is instantiated, then so are all the other classes up to and including Object. Let's look at the constructor of class B.

B(int b){   ///here is my bug
a=b
}

This is the same as:

B(int b){   ///here is my bug
        super();
a=b
}

So, either you have to create a no-argument constructor in class A or amend your code like this to invoke the constructor in class A:

B(int b){   ///here is my bug
        super(b);
a=b
}

[alex lotel]

thanks