לפניכם המחלקות One ו- Two:

java
1public class One
2{
3    private static int num = 0;
4    protected int x;
5
6    public One (int n)
7   {
8          this.x = n;
9          num += n;
10          System.out.println ("One 1");
11    }
12
13    public One (int n1, int n2)
14   {
15          this.x = n1+n2;
16          num += n1;
17          System.out.println ("One 2");
18    }
19
20    public int getNum()
21   {
22          return num;
23    }
24
25    public int getX()
26   {
27          return x;
28    }
29
30    public int mul(int n)
31   {
32          return this.x * n;
33    }
34
35    public void add(One other)
36   {
37          this.x += other.x;
38          System.out.println("x = "+ this.x);
39    }
40}
41
42public class Two extends One
43{
44    private int y;
45    public Two (){
46        super(10);
47        this.y = 12;
48    }
49    public Two (int num)
50    {
51        super (num/2);
52        this.y = num;
53        System.out.println ("Second");
54    }
55
56    public int mul()
57   {
58        return this.x * this.y;
59    }
60
61    public void add (One other)
62    {
63          if (other instanceof Two)
64                 this.y += ((Two)other).y;
65          System.out.println("y = "+ this.y);
66    }
67}

נתונה המחלקה Tester:

java
1public class Tester
2{
3    public static void main(String[] args)
4    {
5        One one1 = new One (1);
6        One one2 = new One (2, 3);
7        One oneTwo = new Two (4);
8        Two two1 = new Two ();
9        Two two2 = new Two (6);
10        // ***
11    }
12}