Question

Class A:

public class A {    

    private String firstName;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

Class B:

public class B extends A{

    private int billNum;

    B(String firstName, String billNum) {
        super(firstName);
        setBillNum(billNum);

    }

    public int getBillNumr() {
        return billNum;
    }

    public void setBillNum(int billNum) {
        this.billNum = billNum;
    }

1.) Now i want to add a default like constructor like B() {}, but i am not allowed to do so. Why is this ?

Answer 1

In the subclass constructor you call a one-argument superclass constructor, which you didn’t declare. Add A(String firstName) { this.firstName = firstName; } to the superclass. Alternatively, replace the line super(firstName); with setFirstName(firstName); in the constructor of B.