In previous articles we have learnt about classes and that a class defines the item we are discussing.  A customer for example does have properies, fields and methods; however it does not not define any customer.  A class therefore provides a mechanism to describe an item, but does not define any real item.  It is thus a blueprint.

In order to create a real customer one has to create an instance of a class and reference it through a variable name.  When creating an instance of the class an object is created in memory.

The line of code below declares a variable theCustomer of data type Customer.  Initially the variable is set to a value of null.  A null variable means there is no real customer, however it is capable of storing a customer

Customer theCustomer;

The code below uses the new keyword to create an object in memory of type Customer. This then sets the variable theCustomer to reference the new object.

   theCustomer = new Customer();

Example

The following example creates three different customer objects in memory and uses them by calling properties and methods.

namespace BrettM.Training.OO.Objects
{
    using System;

    /// <summary>
    /// The customer class defines a business client that purchases
    /// products and services from our company.
    /// </summary>
    class Customer
    {
        #region // Fields

        /// <summary>
        /// A field variable to hold the customers name
        /// </summary>
        private string _name;

        #endregion

        #region // Properties

        /// <summary>
        /// The name of the customer
        /// </summary>
        public string Name
        {
            // The get accessor to return the name field
            get { return _name; }
            // A set accessor to change the name field
            set { _name = value; }
        }

        #endregion

        #region // Methods

        public void Print()
        {
            Console.WriteLine("Customer details");
            Console.WriteLine("----------------");
            Console.WriteLine("Name: {0}", this.Name);
            Console.WriteLine();
        }

        #endregion
    }

    class Program
    {
        static void Main(string[] args)
        {
            //Create a variable of type customer
            Customer theCustomer;
            // Create an instance of the class
            theCustomer = new Customer();

            // Create the customer one object
            Customer one = new Customer();
            one.Name = "Mr Tom Jones";

            // Create the customer two object
            Customer two = new Customer();
            two.Name = "Mrs Sue Smith";

            // Create the customer three object
            Customer three = new Customer();
            three.Name = "Ms Sally Wilson";

            //Print out all customer details
            one.Print();
            two.Print();
            three.Print();
        }
    }
}