避免代码重复

class Foo
{
    public Foo(String myString,Int32 myInt){
        //Some Initialization stuff here
    }

    //Default value for myInt
    public Foo(String myString) : this(myString,42){}

    //Default value for both
    public Foo() : this("The Answer",42){}
}

强制执行良好的封装

public abstract class Foo
{
    protected Foo(String someString)
    {
        //Important Stuff Here
    }
}

public class Bar : Foo
{
    public Bar(String someString,Int32 myInt): base(someString)
    {
        //Let's the base class do it's thing
        // while extending behavior
    }
}