Double value used as argument for the StringBuilder's deleteCharAt() method

Question

I'm preparing for Oracle Associate Certification and am reading the following book :

Oracle Certified Associate, Java SE7 Programmer Study Guide

At the page 77, there is a knowledge test with the following question :

Given the following declaration :

StringBuilder sb = new StringBuilder();

Which of the following are valid uses of the sb variable?

a. sb.append(34.5); b. sb.deleteCharAt(34.5); c. sb.toInteger(3); d. sb.toString();

I assumed the right answers were a & d.

But here's the answer from the book :

a, b, and d There is no StringBuilder toInteger method.

With no other explanation.

So, I went to check the Source Code and here it is :

279    public StringBuilder deleteCharAt(int index) {
280        super.deleteCharAt(index);
281        return this;
282    }

Taking an int as an argument and the method is not overloaded anywhere else.

Do you know an explanation to this "correction" in the book?

Answer 1

It is a mistake in the book. Your answer is correct, it should be only a & d. Here is a link, https://www.packtpub.com/books/content/support/10143 and find the following errata heading (about midway in the page): Errata type: Technical | Page number: 297 | Errata date: 5 Feb 2013

Answer 2

For the example given above sb.deleteCharAt(34.5)

The compiler says

The method deleteCharAt(int) in the type StringBuilder is not applicable for the arguments (double)

Then the book's answer is wrong.