userdatabasefactory.cs

模拟银行系统的实现

using System;
using System.Collections.Generic;
using System.Text;

namespace Project1
{
    public class UserDatabaseFactory
    {
        private static UserDatabase DB_INSTANCE = createInstance();

        /// <summary>
        /// Create an instance of the UserDatabase
        /// </summary>
        /// <returns>An instance of the UserDatabase</returns>
        private static UserDatabase createInstance()
	    {
		    try
		    {
			    UserDatabase userDatabase = new UserDatabaseImp();

			    return userDatabase;
		    }
		    catch (Exception e)
		    {
			    Console.WriteLine(e.ToString());
                return null;
		    }
	    }

        /// <summary>
        /// Get an instance of user database
        /// </summary>
        /// <returns>an instance of UserDatabase</returns>
	    public static UserDatabase getDatabaseInstance()
	    {
	    	return DB_INSTANCE;
	    }
	    	    
	    /// <summary>
	    /// Make sure this class cannot be initialized
	    /// </summary>
        private UserDatabaseFactory()
	    {
		    // do nothing
	    }
    }
}