About Question enthuware.ocajp.i.v7.2.1208 :

[ETS User]

The third answer is correct. A constructor is defined in B, so there are no problems

[admin]

No, it is not correct. It has the same problem as option 2. In case of option 2, there is no constructor provided explicitly so the compiler provides one implicitly. The one that it provides has the same signature as the constructor specified in option 3. So basically, option 2 and 3 are same.

HTH,
Paul.

[kecker]

ETS User, I thought so at first too, but try coding it up.

For example:

Code: Select all

class A{
  protected int i;
  A(int i) {
    this.i = i;
    System.out.println("A i");
  }

}

class B extends A{

  B(){
    System.out.println("B");
  }

  public static void main(String args[]){
    System.out.println("Starting Main");

    B b = new B();
  }
}

You'll get an error, but just add a simple A(){} to the A class and it works. I needs that no-arg constructor, unless you explicitly call super(1); or something like that.

[fasty23]

So, if a super class does not have a no argument constructor, sub class could not have a no argument constructor?

[admin]

So, if a super class does not have a no argument constructor, sub class could not have a no argument constructor?

No, that is not what it says. Subclass can still have a no args constructor like this:
Subclass(){
super(pass some parameter here); //explicitly invoke available constructor of superclass
}

[bsterhiha]

Option 4 : class B { B() {} } is said to be correct but it doesn't compile. Because implicit super constructor A() is undefined. So there is only one option possible

[admin]

Why would it need super class's constructor? B doesn't extend A in this option.

[bsterhiha]

oops It's my fault. Actually B doesn't extends A. option 4 is OK