Why is the answer to K&B 4.8 exclusively correct?

[Harry Henriques]

Hi, The solution to problem 8 in chapter 4 of K&B SCJP 1.5 Certification Text is duplicated in the following code. Why is this code the only possible answer to this problem? For instance, look at the alternative solution below the book's solution. Can you help me out here? Thanks.

class Incr {
public static void main(String[] args) {
Integer x = 7;
int y = 2;
x *= x;
y *= y;
y *= y;
x -= y;
System.out.println(x);
}
} 

class Incr {
public static void main(String[] args) {
Integer x = 7;
int y = 2;
x -= y;
x *= y;
x *= y;
y *= y;
System.out.println(x);
}
} 

[Lukas Sieradzki]

At the end x must be 33...

Your alternative answer is legal for Java, but the result is NOT 33 for x.