Posted on by kpark

Private constructor vs Protected constructor

private constructor는 정적 메소드와 속성 (static method & property)만 있는 경우 사용함.
http://msdn.microsoft.com/en-us/library/vstudio/kcfb85a6.aspx

public class Counter
{
private Counter() { }
public static int currentCount;
public static int IncrementCount() { return ++currentCount; }
}
class TestCounter
{
static void Main()
{
// If you uncomment the following statement, it will generate
// an error because the constructor is inaccessible:
// Counter aCounter = new Counter(); // Error
Counter.currentCount = 100;
Counter.IncrementCount();
Console.WriteLine(“New count: {0}”, Counter.currentCount);
// Keep the console window open in debug mode.
Console.WriteLine(“Press any key to exit.”);
Console.ReadKey();
}

} // Output: New count: 101

protected constructor는 추상클래스 (abstract class)에서 사용을 권고함. 추상 클래스를 상속받는 파생클래스에서 파생 클래스 생성자가 부모 클래스 즉, 추상 클래스를 초기화 하기 위해 추상 클래스 생성자를 호출 할 수 있도록 지원함.
http://msdn.microsoft.com/en-us/library/bcd5672a%28v=vs.80%29.aspx
http://msdn.microsoft.com/ko-kr/library/ms229047(v=vs.100).aspx

public abstract class Shape
{
protected Shape(string name) { this.name = name; }
private string name;
public virtual void Print() { Console.Write(this.name); }
}
public class Triangle: Shape
{
public Triangle(string name): base(name) { this.bottom = 1; this.height = 1 }
private double bottom, height;
public override void Print()
{
base.Print();
Console.WriteLine(” 밑변: {0} 높이: {1}”, this.bottom, this.height);
}
}
public class Rectangle: Shape
{
public Rectangle(string name): base(name) { this.width = 2; this.height = 3 }
private double width, height;
public override void Print()
{
base.Print();
Console.WriteLine(” 가로: {0} 세로: {1}”, this.width, this.height);
}
}
class ShapeTest
{
static void Main()
{
// Shape s = new Shape(“도형”); // Error CS0144, Cannot create an instance of the abstract class
Shape s = new Triangle(“삼각형”);
s.Print(); // 삼각형 밑변: 1 높이: 1
s = new Rectangle(“직사각형”);
s.Print(); // 직사각형 가로: 2 세로: 3
}
}