Methods that don't change a variable's value need to be synchronized if they accessed the variable

Question

From page 231 of OCP Java SE 6 Programmer Practice Exams, question 56:

public class Buffalo {
    protected int y;
    public int getY() { return y; }
    public void setY(int newY) { y = newY; }
}

Which methods need to be synchronized to make the class thread safe?

And the book says that the correct answer is - all of them:

Even methods that don't change a variable's value need to be synchronized if they accessed the variable.

Why I need to synchronize getY()?

It's not changing the state, so it can't cause any synchronization problems, isn't it?