#674 – Can Overload If Parameters Differ Only by ref Modifier

September 19, 2012 Leave a comment

You can overload methods, i.e. create two methods with the same name, if the methods have different parameter lists, where the lists differ in the number or type of the parameters.  For example:

        public void Fetch(Bone b)
        {
            Console.WriteLine(string.Format("Fetching bone {0}", b.Description));
        }

        public void Fetch(Dog d)
        {
            Console.WriteLine(string.Format("I'll go get {0}", d.Name));
        }

You can also overload methods if they differ only in their use of the ref modifier.  One method can accept a parameter passed by value and you can have another version of the method that allows passing the parameter by reference.

        public void Bark(string sound)
        {
            Console.WriteLine(sound);
        }

        public void Bark(ref string sound)
        {
            Console.WriteLine(sound);

            // Update caller's copy of sound variable
            sound = sound + "!";
        }

            Dog d = new Dog("Rex", 3);
            string sound = "woof";
            d.Bark(sound);
            d.Bark(ref sound);   // woof!
            d.Bark(ref sound);   // woof!!
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Filed under Methods Tagged with , , ,

#673 – Types Used in using Statement Must Implement IDisposable

September 18, 2012 Leave a comment

The using statement is a shortcut for a try/finally block where the Dispose method is automatically called on any objects instantiated as part of the using statement.

            using (StreamWriter sw = new StreamWriter(@"D:\Hi.txt"))
            {
                sw.Write("Hi !");
            }
            // StreamWriter.Dispose automatically called

Because the Dispose method is called automatically on all objects instantiated as part of the using statement, each object must belong to a type that implements IDisposable.  The example below leads to a compile-time error because Dog does not implement IDisposable and therefore does not have a Dispose method.

            using (Dog d = new Dog("Kirby", 15))
            {
                d.Bark();
            }

Filed under Basics Tagged with , , , , ,

#672 – An Exception Thrown From a Finalizer Will Be Treated as an Unhandled Exception

September 17, 2012 Leave a comment

If an exception originates in a finalizer in C# and is not handled within the body of the finalizer, the exception will be treated by the application as an unhandled exception.  If you have no mechanism for dealing with unhandled exceptions, this will lead to a crash.

In the example below, the exception originating in the Dog finalizer is not caught within the Main method.

        static void Main()
        {
            try
            {
                Dog d = new Dog();
                d = null;

                GC.Collect();
                GC.WaitForPendingFinalizers();

                Console.WriteLine("I made it to the end of the program");
                Console.ReadLine();
            }
            catch (Exception xx)
            {
                Console.WriteLine(string.Format("Hey, I caught an exception! {0}", xx.ToString()));
            }

    public class Dog
    {
        public Dog()
        {
            Console.WriteLine("Dog constructor");
        }

        ~Dog()
        {
            Console.WriteLine("Dog finalizer running");
            throw new Exception("** Exception from Dog finalizer **");
        }
    }

Filed under Exceptions Tagged with , ,

#671 – A Base Class Constructor Can Call a Virtual Method

September 14, 2012 1 Comment

If a base class constructor calls a virtual method that is overridden in a derived class, the version of the method in the derived class is the one that will get called.

For example, assume that we have a Dog class that defines a virtual Bark method and a Terrier subclass that overrides the Bark method.

    public class Dog
    {
        public Dog()
        {
            Console.WriteLine("Dog constructor");
            Bark();
        }

        public virtual void Bark()
        {
            Console.WriteLine("Woof");
        }
    }

    public class Terrier : Dog
    {
        public Terrier()
            : base()
        {
            Console.WriteLine("Terrier constructor");
        }

        public override void Bark()
        {
            Console.WriteLine("Terrier barking!");
        }
    }

Assume you create an instance of a Terrier.

            Terrier t = new Terrier();

The Terrier constructor calls the Dog constructor, which invokes the Bark method.  But it’s the Bark method in Terrier that is called, rather than the Bark method in Dog.

Filed under Classes Tagged with , , ,

#670 – Static vs. Instance Initialization

September 13, 2012 Leave a comment

Static fields and properties are data members associated with a class itself, rather with instances of that class.  A static constructor can be used to initialize static members.  Static fields can also be initialized when they are declared.

The first time that you reference a static member, the following occurs:

  • All static fields are initialized
  • The static constructor is called
  • Your code, which accesses the static member, executes

If you reference an instance method, or create an instance of the class, before referencing any static members, the following occurs:

  • All static fields are initialized
  • The static constructor is called
  • All instance fields are initialized
  • The instance constructor is called
  • Your code, which accesses an instance member, executes

For example, initializing an instance of a Dog leads to the output shown below.

Dog d = new Dog();

Filed under Classes Tagged with , , , , ,

#669 – Initializing Fields by Calling A Method

September 12, 2012 Leave a comment

You can initialize fields in a class at the point where you declare them, using a constant.  You can also initialize a field to a value returned from a call to a method–as long as the method is not an instance method within the same class.

Here’s an example, where we call a static method in the same class to initialize a field.

    public class Dog
    {
        private static string GenerateCreationInfo()
        {
            return string.Format("I was created at {0}", DateTime.Now);
        }

        public string CreationInfo = GenerateCreationInfo();

        public string Name { get; set; }
        public int Age { get; set; }

        public Dog(string name, int age)
        {
            Name = name;
            Age = age;
        }
    }

Filed under Classes Tagged with , , ,

#668 – GetTotalMemory Indicates How Much Memory You’ve Allocated

September 11, 2012 2 Comments

You can call the GC.GetTotalMemory function to find out the total # bytes you’ve allocated so far on the managed heap.  Note that this number does not include other memory that your process may have allocated, including things like memory allocated in unmanaged code.

        static void Main()
        {
            try
            {
#if DEBUG
                GC.Collect();
#endif
                Console.WriteLine(string.Format("Before we start, total mem alloc'd {0} bytes", GC.GetTotalMemory(false)));

                while (true)
                {
                    ConsoleKeyInfo cki = Console.ReadKey();

                    int size = 1024 * 1024 * 100;  // 100MB
                    byte[] data = new byte[size];

                    Array.Clear(data, 0, size);

                    _bigList.Add(data);

#if DEBUG
                    GC.Collect();
#endif
                    Console.WriteLine(string.Format("Total mem alloc'd now {0} bytes", GC.GetTotalMemory(false)));
                }
            }
            catch (Exception xx)
            {
                Console.WriteLine(xx.ToString());
                Console.ReadLine();
                }
        }

Filed under Basics Tagged with , , , ,

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