#291 – No Default Constructor if You Define any Constructors

If you don’t define any constructors in a class, the compiler automatically generates a default parameterless constructor.  You can then create a new instance of the object without passing any parameters.

            Dog d1 = new Dog();

If you define at least one constructor, the compiler no longer generates a parameterless constructor.

Below, we define a single constructor for Dog, accepting a name parameter.

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

        public Dog(string name)
            Name = name;
            Age = 1;

Now we can define a new instance of Dog by passing in a name parameter.  But we can no longer create a new instance using no parameters.

            Dog d1 = new Dog("Rin Tin Tin");

            // Compiler error: Dog does not contain a constructor
            //   that takes 0 arguments.
            Dog d2 = new Dog();

About Sean
Software developer in the Twin Cities area, passionate about .NET technologies. Equally passionate about my own personal projects related to family history and preservation of family stories and photos.

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