Constructor Issues

[John Paterson]

Hi Guys,

The following code compiles fine:

Fruit class

public class Fruit {

    Fruit()
    {
        
    }
    Fruit(String a) {
        String b = a;
    }
}

Apple class

public class Apple extends Fruit{   

   
    void hello()
    {
        System.out.println("Hi");
        
    }
       
}

However if I remove the no argument constructor from the Fruit class, I run into problems. I am getting the following error:

constructor Fruit in class fruits.Fruit cannot be applied to given types;
required: java.lang.String
found: no arguments
reason: actual and formal argument lists differ in length

I am not sure why, hope someone can advise. Thanks.


regards
John

[Winston Gutkowski]

John Paterson wrote:I am not sure why, hope someone can advise. Thanks.

Since you didn't do it yourself, the compiler
(a) Adds a public no-args constructor to any class that doesn't have any.
(b) Adds super() as the first line of any constructor that doesn't already have a super() call (of any kind).

Therefore, your Apple class actually looks like:

public class Apple extends Fruit {
   public Apple() {
      super();
   }
   ...
}

Make sense now?

Winston

[John Paterson]

Hi Winston Gutkowski

Thanks for the reply. You mean to say super() was actually looking for a no-argument constructor in the Fruit superclass and since it didn't find any it gave that error?

regards
John

[Jeff Verdegan]

John Paterson wrote:Hi Winston Gutkowski

Thanks for the reply. You mean to say super() was actually looking for a no-argument constructor in the Fruit superclass and since it didn't find any it gave that error?

regards
John

Correct.

Any constructor (except in the Object class) that doesn't explicitly calls super(...) or this(...) as its first statement gets a call to no-arg super() inserted by the compiler. If that super() doesn't exist, it's an error.

Additionally, if you don't provide any constructor at all in your class, then, as Winston explained, the compiler inserts a no-arg constructor that does nothing but call the no-arg super().

[John Paterson]

Hi

Noted. Thanks Jeff Verdegan

regards
John