Understanding which constructor is chosen and why

Question

Why following program every time prints I\'m string and not I\'m object. or I\'m int.?

public class Demo {

    public         


        

Answer 1

The fact the String constructor is mentioned in by the compiler in your second error:

The constructor Demo(String) is ambiguous.

is not significant. This is because the Constructor which takes a String is the first declared constructor, so the compiler uses it in its error message. Change to have the Object constructor first and you get:

The constructor Demo(Object) is ambiguous.

What it's trying to say is there's ambiguity between the constructor which takes the Integer and the Object, so you have to be more specific, as null can be applied to each. Integer IS-NOT-A String, so the two types are not compatible. You need to be more specific so the compiler can bind the constructor call.

See @Jon Skeet answer for why the compiler raises an error in some instances and not in others.