How many variables should a constructor have?

Question

I realize this is a pretty open question and could get a variety of answers, but here goes.

Using C# (or Java, or any OO language), is there a general rule that states how many variables should be passed into the constructor? The number of variables I am passing into the constructor of the extended classes seem to be getting out of hand.

In an effort to encapsulate the data of a class, I declare the members private, initialize them in my constructor, and use public accessors.

Here is an example:

public class A {   private int var1;   private int var2;   private int var3;    //3 variables passed in   public A(int v1, int v2, int v3)   {     var1 = v1;     var2 = v2;     var3 = v3;   }    //Properties (accessors) here }  public class B : A {   private int var4;   private int var5;    //5 variables passed in   public B(int v1, int v2, int v3, int v4, int v5)   : base(v1,v2,v3)   {     var4 = v4;     var5 = v5;   }    //Properties (accessors) here }  public class C : B {   private int var6;   private int var7;    //7 variables passed in !!!   public C(int v1, int v2, int v3, int v4, int v5, int v6, int v7)   : base(v1,v2,v3,v4,v5)   {     var6 = v6;     var7 = v7;   }    //Properties (accessors) here } 

My constructors are usually passing in different objects, not just ints. I started questioning my design when I started passing in 7 variables to the constructor of the child class, but I have also had trouble figuring out a different way to do this.

Is this considered bad programming practice? Is there a general limit to the number of variables you should pass into a constructor?

Answer 1

For me, the correct answer is:

You should pass in as many variables as is required to setup the object in a state that is not invalid.

Anything else that is "option", I prefer to leave as properties, especially now that C# provides object initializers.