Data from file into ArrayList

Hello,

I have written a program which includes this code

Code :

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.ArrayList;
import java.util.HashSet;
 
/**
 * The purpose of this class is to be an
 * ArrayList manager. It helps manage the
 * ArrayLists and the HashSet and have
 * access to them and their data.
 */
public class ArrayListManager {
 
 
    private ArrayList<Admin> admin;
    private ArrayList<Manager> manager;
    private ArrayList<Employee> employee;
    private ArrayList<Keyboard> keyboard;
    private ArrayList<Mouse> mouse;
    private ArrayList<Printer> printer;
    private ArrayList<StorageUnit> storageUnit;
    private ArrayList<Order> order;
    private HashSet<String> mySet;
 
/**
     * This is the constructor of the class ArrayListManager. 
     * It creates eight different arraylists and one HashSet.
     */
    public ArrayListManager()
    {
        admin = new ArrayList<Admin>();
        manager = new ArrayList<Manager>();
        employee = new ArrayList<Employee>();
        keyboard = new ArrayList<Keyboard>();
        mouse = new ArrayList<Mouse>();
        printer = new ArrayList<Printer>();
        storageUnit = new ArrayList<StorageUnit>();
        order = new ArrayList<Order>();
        mySet = new HashSet<String>();
    }
 
    /**
     * This function returns an admin ArrayList.
     * @return The list with the administrators.
     */
    public ArrayList getArrayAdmin()
    {
        return admin;
    }
 
    /**
     * This function returns a manager ArrayList.
     * @return The list with the managers.
     */
    public ArrayList getArrayManager()
    {
        return manager;
    }
 
    /**
     * This function returns an employee ArrayList.
     * @return The list with the employees.
     */
    public ArrayList getArrayEmployee()
    {
        return employee;
    }
 
    /**
     * This function returns the ArrayList keyboard.
     * @return The list with the keyboards.
     */
    public ArrayList getArrayKeyboard()
    {
        return keyboard;
    }
 
    /**
     * This function returns the ArrayList mouse.
     * @return The list with the mice.
     */
    public ArrayList getArrayMouse()
    {
        return mouse;
    }
 
    /**
     * This function returns the ArrayList printer.
     * @return The list with the printers.
     */
    public ArrayList getArrayPrinter()
    {
        return printer;
    }
 
    /**
     * This function returns the ArrayList storageUnit.
     * @return The list with the storage units.
     */
    public ArrayList getArrayStorageUnit()
    {
        return storageUnit;
    }
 
    /**
     * This function returns the ArrayList order.
     * @return The list with the orders.
     */
    public ArrayList getArrayOrder()
    {
        return order;
    }
 
 /**
     * This functions gets the data from the files Admin.dat, Manager.dat, Employee.dat,
     * Keyboard.dat, Mouse.dat, Printer.dat, StorageUnit.dat, Order.dat and MySet.dat.
     * In this way, any changes that had been saved during a previous execution of the
     * programme are loaded again.
     */
    public void getData() {
		FileInputStream fis = null;
		ObjectInputStream in = null;
		try {
			fis = new FileInputStream("Admin.dat");
			in = new ObjectInputStream(fis);
			admin = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
		try {
			fis = new FileInputStream("Manager.dat");
			in = new ObjectInputStream(fis);
			manager = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
                try {
			fis = new FileInputStream("Employee.dat");
			in = new ObjectInputStream(fis);
			employee = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
                try {
			fis = new FileInputStream("Keyboard.dat");
			in = new ObjectInputStream(fis);
			keyboard = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
                try {
			fis = new FileInputStream("Mouse.dat");
			in = new ObjectInputStream(fis);
			mouse = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
                try {
			fis = new FileInputStream("Printer.dat");
			in = new ObjectInputStream(fis);
			printer = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
                try {
			fis = new FileInputStream("StorageUnit.dat");
			in = new ObjectInputStream(fis);
			storageUnit = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
                try {
			fis = new FileInputStream("Order.dat");
			in = new ObjectInputStream(fis);
			order = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}
 
	}
}

Instead of having this code reiteration at getData function, I would like to write a function getData(ArrayList array, String filename).

Code :

public void getData(ArrayList array, String filename) {
		FileInputStream fis = null;
		ObjectInputStream in = null;
		try {
			fis = new FileInputStream(filename);
			in = new ObjectInputStream(fis);
			array = (ArrayList) in.readObject();
			in.close();
		} catch (IOException ex) {
			ex.printStackTrace();
		} catch (ClassNotFoundException ex) {
			ex.printStackTrace();
		}

The problem with this function is when I try to load the data form the files to the arraylists.

At my main class I call this function by writting

Code :

ArrayListManager list = new ArrayListManager();
list.getData(list.getArrayAdmin(), "Admin.dat");
list.getData(list.getArrayManager(), "Manager.dat");
....
list.getData(list.getArrayStorageUnit(), "StorageUnit.dat");

The problem is that when I print the size of the arraylists using the function list.getArrayAdmin().size(), it is 0 which shows that the data is not loaded.

I would appreciate your help.