How can I transfer some values from one class to another?

Question

Firstly I have 3 classes with getters and setters. In the Main class I scan two variables of type int called rows and columns , which are in turn used to initialise an instance of the Airplane class. After this I want to calculate the product of these variables in class Flight . So I gave the values rows = 2 and columns = 3 and it printed 0 to the console . Every different value I give keeps returning 0 as a result. Your help will be appreciated! Here is my code:

Main class:

  public class Main {
       public static void main(String[] args) {
           int counter=1;
           if (counter==1) {
               Scanner scanner = new Scanner(System.in);
               int rows, columns;
               Airplane airplane = new Airplane();
               rows = scanner.nextInt();
               airplane.setRows(rows);
               columns = scanner.nextInt();
               airplane.setColumns(columns);
               System.out.println(airplane.getColumns()*airplane.getRows());
               counter++;
           }
           if (counter==2){
                   Flight flight = new Flight();
                   int seats=0;
                   seats=flight.getNumberOfSeats();
                   System.out.println(seats);
            }
    }
}

Flight class:

public class Flight {
    private int numberOfSeats;
    //getters and setters
}

Airplane class:

public class Airplane {
    private int rows;
    private int columns;
    //getters and setters
}

Answer 1

In the second if statement you created a new instance of Flight and you haven't changed any of its field values, so consequently when you are reading the number of seats here it still has the initial value 0 (the default value for an int). The code below should do what you want.

public class Main {
   public static void main(String[] args) {
       int counter=1;
       Airplane airplane;
       if (counter==1) {
           Scanner scanner = new Scanner(System.in);
           int rows, columns;
           airplane = new Airplane();
           rows = scanner.nextInt();
           airplane.setRows(rows);
           columns = scanner.nextInt();
           airplane.setColumns(columns);
           System.out.println(airplane.getColumns()*airplane.getRows());
           counter++;
       }
       if (counter==2) {
           Flight flight = new Flight();
           flight.setNumberOfSeats(airplane.getColumns()*airplane.getRows());
           System.out.println(flight.getNumberOfSeats());
       }
   }
}

Answer 2

I think this is an exercise in polymorphism and composition . It is likely that the idea is that a Flight has an Airplane HAS-A relation . Your Flight class will than look like this:

class Flight {
  private Airplane airplane;
  private int numberOfSeats;

  public Flight(Airplane airplane) {
    this.airplane = airplane;
    this.numberOfSeats = (airplane.getColumns() * airplane.getRows());
  }

  public void getNumberOfSeats() {
     return this.numberOfSeats;
  }


  public void setNumberOfSeats(int numberOfSeats) {
    this.numberOfSeats = numberOfSeats;
  }
}

In your main code you now only have to pass the reverence of the Airplane to the Flight .

Flight flight = new Flight(airPlane);

Since you already defined the plane outside the if scope this can be done, if you change it to Airplane airplane = null;