Question

I program on netbeans ubuntu java standart project (test preparation).
when I create AccountStudent.java I get error.

Account.java

public abstract class Account {
 protected double _sum;
 protected String _owner;
 protected static int accountCounter=0;

 public Account(String owner){
     this._sum=0;
     this._owner=owner;
     accountCounter++;
 }
}

AccountStudent.java– error: cannot find symbol: constructor Account()

public class AccountStudent extends Account{

}

Fix for problem- add empty Account constructor:

Account.java

public abstract class Account {
 protected double _sum;
 protected String _owner;
 protected static int accountCounter=0;

 public Account(){

 }

 public Account(String owner){
     this._sum=0;
     this._owner=owner;
     accountCounter++;
 }
}

Why should i create empty constructor Account if already he exist because he inherit Object class?

Thanks

Answer 1

Why should i create empty constructor
Account if already he exist because he
inherit Object class?

Constructors are not inherited. If a class has no explicit constructor, hte compiler silently adds a no-argument default constructor which does nothing except call the superclass no-argument constructor. In your case, that fails for AccountStudent because Account does not have a no-argument constructor. Adding it is one way to resolve this. Another would be to add a constructor to AccountStudent that calls the existing constructor of Account, like this:

public class AccountStudent extends Account{
    public AccountStudent(String owner){
        super(owner);
    }
}