I have hit a little problem with constructors at my program. It is a simple bank database which stores customer data. I have to implement methods for depositing, withdrawing and transferring cash between two accounts. I have implemented that kind of constructor to add new bank account:
public Customer() {
Scanner scan = new Scanner(System.in);
System.out.println("Enter id of customer:");
this.id = scan.nextLine();
File folder = new File("CustomerDataBase" + File.separator + this.id + ".txt");
if(folder.exists()) {
System.out.println("Customer ID already exists!");
System.exit(1);
}
try {
System.out.println("Enter name of customer:");
this.name = scan.nextLine();
System.out.println("Enter surname of customer:");
this.surname = scan.nextLine();
System.out.println("Enter PESEL number of customer:");
this.pesel = scan.nextLine();
System.out.println("Enter address of customer:");
System.out.println(" Street:");
this.adressStreet = scan.nextLine();
System.out.println(" City:");
this.adressCity = scan.nextLine();
System.out.println(" Zip Code: ");
this.zipCode = scan.nextLine();
System.out.println("Enter funds of Customer:");
this.funds = Double.parseDouble(scan.nextLine());
this.saveCustomer();
scan.close();
}catch(NumberFormatException e) {
System.out.println("Error : " + e);
System.exit(1);
}
}
And then I have a method withdraw :
static void withdraw (int amount, int id) {
File f = new File("CustomerDataBase" + File.separator + String.valueOf(id) + ".txt");
Scanner fRead;
Customer tempCustomer = new Customer();
try{
fRead = new Scanner(f);
tempCustomer.id = fRead.nextLine();
tempCustomer.name = fRead.nextLine();
tempCustomer.surname = fRead.nextLine();
tempCustomer.pesel = fRead.nextLine();
tempCustomer.adressStreet = fRead.nextLine();
tempCustomer.adressCity = fRead.nextLine();
tempCustomer.zipCode = fRead.nextLine();
tempCustomer.funds = Double.parseDouble(fRead.nextLine()) - id;
fRead.close();
tempCustomer.saveCustomer();
}catch(FileNotFoundException e) {
System.out.println("File not found!");
System.exit(1);
}
}
The withdraw method reads data from file and have to stores it in class. So I'm creating object as customer type. But I want to use just "plain" (default) constructor which Java provides when you do not declare your own.
How to do that? I read about super(): statement, but if I understood it right, it works only when you inherit from another class.
Every class comes with a default constructor that is not visible in the class itself. However, please note that if you specify a constructor other than the default constructor, the default constructor can't be used, per @Rustam comment below. For example, let's say your Customer class looks like this:
public class Customer {
private String name;
private String lastName;
private age int;
private String ssn;
//default constructor that is NOT visible
Customer()
{
}
//other constructor given name and lastName
Customer(name, lastName)
{
this.name = name;
this.lastName = lastName;
}
//getters and setters
}
The constructor Customer() is created by default and it is not necessary for you to include in your class.
You can then create a customer instance using the default constructor and then you would need to use setters to set the properties, like follows:
public class Test {
public static void main(String [] args){
Customer c = new Customer();
//setting parameters
c.setName("Jose");
c.setLastName("Mejia");
}
}