Chapter 13.3, Problem 13.3.4CP

What is wrong in the following code? (Note the compareTo method for the Integer and Double classes was introduced in Section 10.7.)

public class Test {

public static void main(String[] args) {

Number x = new Integer(3);

System.out.println(x.intValue());

System.out.println(x.compareTo(new Integer(4)));

}

}