CODEWITHSUNDEEP
javaconstructor
Tony Wolff
Tony Wolff

Reputation: 742

How to extend a class with a different constructor?

I am having difficulty extending a person class to a patient class

I have a Person class with a constructor looking like 

  public Person(String firstname,String surname) {
        fFirstname=firstname;
        fSurname=surname;
    }

I then have a Patient Class

public class Patient extends Person

I want to have a constructor for a patient looking roughly like

public Patient(String hospNumber) {
    fFirstname = lookup(hospNumber,"firstname");
    fSurname = lookup(hospNumber,"surname");
}

However I get a complaint that the Patient constructor needs (String,String). I can see why this is, but can't see how to extend the person class for a patient.

Upvotes: 4

Views: 320

Answers (3)

nick zoum
nick zoum

Reputation: 7325

Change the patient constructor to this. 

public Patient(String hospNumber) {
   super(lookup(hospNumber,"firstname"), lookup(hospNumber,"surname"));
}

But the lookup method needs to be static in order to do this. Otherwise you will have to change it to:

public Patient(String hospNumber, String firstname, String surname) {
  super(firstname,surname);
}

Or something similar.

Finally you could also add another constructor to the Person class. like Person() and set the rest of the details later. this way you don't have to even write super() on the constructor of the patient.

Side notes: A class can have more than 1 constructors as long as they do not have the same parameters.

super() calls the constructor of the super-class (that class from which this class inherits).

Upvotes: 2

Arjit
Arjit

Reputation: 3456

Either you can have a default constructor in Person class

public Person() {

}

Or

You need to call constructor the Person class using super method as its a 2-arg constructor

public Patient(String hospNumber) {
    super(lookup(hospNumber,"firstname"), lookup(hospNumber,"firstname"));
}

Upvotes: 2

yshavit
yshavit

Reputation: 43456

Just pass the result of those two method calls to the super constructor:

public Patient(String hospNumber) {
    super(lookup(hospNumber,"firstname"), lookup(hospNumber,"surname"));
}

Those methods have to be static, since the this they would otherwise been called on hasn't been constructed yet when they're invoked.

Upvotes: 5

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