לפניכם המחלקות First ו-Second שהמחלקה Second יורשת מהמחלקה First, והמחלקה Tester עם הפעולה main ובה חמש הצהרות עצמים ולאחריהן הערה // ***, המסמנת מיקום להוספת פקודה.

public class First
{
    private static int count = 0;
    protected int x;
    protected int y;
    public First (int num) {
        this.x = num;
        this.y = num;
        count ++;
        System.out.println ("First 1");
    }
    public First (int num1, int num2) {
        this.x = num1;
        this.y = num2;
        count ++;
        System.out.println ("First 2");
    }
    public static int getCount() { return count; }
    public int getX() { return x; }
    public int getY() { return y; }
    public int sum() { return this.x + this.y; }
    public void add(First other) {
        this.x += other.x;
        this.y += other.y;
        System.out.println("x = " + this.x + " y = "+ this.y);
    }
}

public class Second extends First
{
    private int z;
    public Second (int num) {
        super (num);
        this.z = num;
        System.out.println ("Second");
    }
    public int sum() { return super.sum() + this.z; }
    public void add (First other) {
        this.x += other.getX();
        this.y += other.getY();
        if (other instanceof Second)
            this.z += ((Second)other).z;
        System.out.println("x = "+ this.x + " y ="+ this.y+ " z ="+this.z);
    }
}

public class Tester
{
    public static void main(String[] args)
    {
        First f1 = new First (40);
        First f2 = new First (40, 50);
        First f3 = new Second (100);
        Second s1 = new Second (100);
        Second s2 = new Second (100);
        // ***
    }
}