/* This class describes a customer with the following attributes and methods! The customer class
 * is abstract as the customer needs to be either a company customer or a private customer. All
 * variables and methods which define the customer and are inherited! */

import java.util.ArrayList;

public abstract class Customer {

	private int customerNbr; // Identification variable!
	private String adress;
	private String city;
	private String areaCode;
	private String phoneNbr;
	private String mailAdress;
	private int discountLevel; // What level of discount the customer has (10%, 20% ...)!
	private ArrayList<Order> previousOrders; // The previous orders!

	public Customer(int customerNbr,
			String adress, String city, String areaCode, String phoneNbr,
			String mailAdress, int discountLevel) {

		this.customerNbr = customerNbr;
		this.adress = adress;
		this.city = city;
		this.areaCode = areaCode;
		this.phoneNbr = phoneNbr;
		this.mailAdress = mailAdress;
		this.discountLevel = discountLevel;
		this.previousOrders = new ArrayList<Order>();
	}

	public int getCustomerNbr() {
		return customerNbr;
	}

	public void setCustomerNbr(int customerNbr) {
		this.customerNbr = customerNbr;
	}

	public String getAdress() {
		return adress;
	}

	public void setAdress(String adress) {
		this.adress = adress;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}

	public String getAreaCode() {
		return areaCode;
	}

	public void setAreaCode(String areaCode) {
		this.areaCode = areaCode;
	}

	public String getPhoneNbr() {
		return phoneNbr;
	}

	public void setPhoneNbr(String phoneNbr) {
		this.phoneNbr = phoneNbr;
	}

	public String getMailAdress() {
		return mailAdress;
	}

	public void setMailAdress(String mailAdress) {
		this.mailAdress = mailAdress;
	}

	public int getDiscountLevel() {
		return discountLevel;
	}

	public void setDiscountLevel(int discountLevel) {
		this.discountLevel = discountLevel;
	}

	public void addPreviousOrder(Order order) {
		previousOrders.add(order);
	}
}

/* This class describes a customer with the following attributes and methods! The customer class
 * is abstract as the customer needs to be either a company customer or a private customer. All
 * variables and methods which define the customer and are inherited! */

import java.util.ArrayList;

public abstract class Customer {

        private int customerNbr; // Identification variable!
        private String adress;
        private String city;
        private String areaCode;
        private String phoneNbr;
        private String mailAdress;
        private String IDNbr;
        private int discountLevel; // What level of discount the customer has (10%, 20% ...)!
        private ArrayList<Order> previousOrders; // The previous orders!

        public Customer(int customerNbr, String IDNbr,
                        String adress, String city, String areaCode, String phoneNbr,
                        String mailAdress, int discountLevel) {

                this.customerNbr = customerNbr;
                this.IDNbr = IDNbr;
                this.adress = adress;
                this.city = city;
                this.areaCode = areaCode;
                this.phoneNbr = phoneNbr;
                this.mailAdress = mailAdress;
                this.discountLevel = discountLevel;
                this.previousOrders = new ArrayList<Order>();
        }

        public int getCustomerNbr() {
                return customerNbr;
        }

        public void setCustomerNbr(int customerNbr) {
                this.customerNbr = customerNbr;
        }

        public String getAdress() {
                return adress;
        }

        public void setAdress(String adress) {
                this.adress = adress;
        }

        public String getCity() {
                return city;
        }

        public void setCity(String city) {
                this.city = city;
        }

        public String getAreaCode() {
                return areaCode;
        }

        public void setAreaCode(String areaCode) {
                this.areaCode = areaCode;
        }

        public String getPhoneNbr() {
                return phoneNbr;
        }

        public void setPhoneNbr(String phoneNbr) {
                this.phoneNbr = phoneNbr;
        }

        public String getMailAdress() {
                return mailAdress;
        }

        public void setMailAdress(String mailAdress) {
                this.mailAdress = mailAdress;
        }

        public int getDiscountLevel() {
                return discountLevel;
        }

        public void setDiscountLevel(int discountLevel) {
                this.discountLevel = discountLevel;
        }

        public void addPreviousOrder(Order order) {
                previousOrders.add(order);
        }

		public String getIDNbr() {
			return IDNbr;
		}

		public void setIDNbr(String IDNbr) {
			IDNbr = IDNbr;
		}
}

Update Customer.java