Doubt about method signature StringBuilder, Chapter 5, page 272 (K&B7)

[Roger Jenkins]

On page 272, regarding the methods in the StringBuilder-class, the headline regarding the toString() method says:
public String toString()

but shouldn't that be:
public StringBuilder toString()

since it is a StringBuilder method and not a String method?

(This post originated in the K&B7 errata thread)

[Roel De Nijs]

Roger Jenkins wrote:but shouldn't that be:
public StringBuilder toString()

since it is a StringBuilder method and not a String method?

You are incorrect! The study guide is spot-on. This is a method signature of the StringBuilder class and if you have a look at the API documentation of the StringBuilder class, you'll notice that the correct method signature of the toString() method is

public String toString()

and not (as you suggested)

public StringBuilder toString()

And if you think about it a little bit, it makes sense: the toString() method is defined in the Object class and defines a String as the return type. Just like in the String class, this method is overridden in the StringBuilder class as well. And to have a valid override you need the same method signature and return type (or a covariant return), so that's why you can't have the method signature you have suggested, because it's an invalid override and also an invalid overload (because the parameter list is not different from the method with the same name defined in the Object class).

Hope it helps!
Kind regards,
Roel

[Roger Jenkins]

Thank you for clearing this up! Yes, it helps!