Fields
A field is a variable that is associated with a class or with an instance of a class.
A field declared with the static modifier defines a static field. A static field identifies exactly one storage location. No matter how many instances of a class are created, there is only ever one copy of a static field.
A field declared without the static modifier defines an instance field. Every instance of a class contains a separate copy of all the instance fields of that class.
In the following example, each instance of the Color class has a separate copy of the r, g, and b instance fields, but there is only one copy of the Black, White, Red, Green, and Blue static fields:
public class Color
{
public static readonly Color Black = new Color(0, 0, 0);
public static readonly Color White = new Color(255, 255, 255);
public static readonly Color Red = new Color(255, 0, 0);
public static readonly Color Green = new Color(0, 255, 0);
public static readonly Color Blue = new Color(0, 0, 255);
private byte r, g, b;
public Color(byte r, byte g, byte b) {
this.r = r;
this.g = g;
this.b = b;
}
}
As shown in the previous example, read-only fields may be declared with a readonly modifier. Assignment to a readonly field can only occur as part of the field’s declaration or in a constructor in the same class.