C#本当に分かったか?

    class Program
    {
        static void Main(string[] args)
        {
            Car theCar = new Car();
            TestClass(theCar);
            Console.WriteLine(theCar.Name);
            TestClass2(theCar);
            Console.WriteLine(theCar.Name);
            TestClass3(theCar);
            Console.WriteLine(theCar.Name);
            Console.ReadLine();

        }

        public static void TestClass(Car mycar)
        {
            mycar.Name = "aaa";
            mycar.Number = 100;
            mycar.ProductArea = "china";
        }

        public static void TestClass2(Car mycar)
        {
            Car thiscar = mycar;
            thiscar.Name = "bbb";
            thiscar.Number = 200;
            thiscar.ProductArea = "Japan";
        }

        public static void TestClass3(Car mycar)
        {
            Car thiscar = new Car(mycar);
            thiscar.Name = "ccc";
            thiscar.Number = 300;
            thiscar.ProductArea = "Korea";
        }
    }

    class Car
    {
        public string Name; 
        public string ProductArea;
        public int Number;

        public Car(Car thecar)
        {
            this.Name = thecar.Name;
            this.Number = thecar.Number;
            this.ProductArea = thecar.ProductArea;
        }
        public Car()
        {
            this.Name = null;
            this.Number = 0;
            this.ProductArea = null;
        }
    }