How to set a default value in class when an object is created

Question

I want to make card number of the customer is always set to -1 when a new customer is created.

Image of how code looks likes

public Customer(int cardNumber, int yearOfBirth) {
    this.cardNumber = cardNumber;
    this.yearOfBirth = yearOfBirth;
}

public int getCardNumber() {
    return cardNumber;
}

public void setCardNumber(int cardNumber) {
    this.cardNumber = cardNumber;
}

Answer 1

This is one way to do it. Add an initializer to the field declaration.

public class Customer {
    private int cardNumber = -1;
    private int yearOfBirth;
    
    public Customer(int yearOfBirth) {
        this.yearOfBirth = yearOfBirth;
    }
    
    public int getCardNumber() {
        return cardNumber;
    }
    
    public void setCardNumber(int cardNumber) {
        this.cardNumber = cardNumber;
    }
}

Another alternative would be to explicitly initialize the field to its default value in the constructor; e.g.

    public Customer(int yearOfBirth) {
        this.yearOfBirth = yearOfBirth;
        this.cardNumber = -1;
    }