Thinking in Java Fourth Edition Bruce Eckel Chapter 5 Exercise 6

class SomeData
{
    protected int a = 13;
}

class DataChanger
{
    static void change(SomeData sd, int i)
    {
        sd.a = i;
    }
}

public class ProtectedData
{
    public static void main(String[] args)
    {
        SomeData x = new SomeData();
        System.out.println(x.a);                   
        DataChanger.change(x, 99);
        System.out.println(x.a);       
    }  
}