ניתוח ירושה ופולימורפיזם

1public class First {
2    private static int count = 0;
3    protected int x;
4    protected int y;
5
6    public First (int num) {
7        this.x = num;
8        this.y = num;
9        count ++;
10        System.out.println ("First 1");
11    }
12    public First (int num1, int num2) {
13        this.x = num1;
14        this.y = num2;
15        count ++;
16        System.out.println ("First 2");
17    }
18    public static int getCount() {
19        return count;
20    }
21    public int getX() { return x; }
22    public int getY() { return y; }
23    public int sum() {
24        return this.x + this.y;
25    }
26    public void add(First other) {
27        this.x += other.x;
28        this.y += other.y;
29        System.out.println("x = "+ this.x + "y = "+ this.y);
30    }
31}
32
33public class Second extends First {
34    private int z;
35    public Second (int num) {
36        super (num);
37        this.z = num;
38        System.out.println ("Second");
39    }
40    public int sum() {
41        return super.sum() + this.z;
42    }
43    public void add (First other) {
44        this.x += other.getX();
45        this.y += other.getY();
46        if (other instanceof Second)
47            this.z += ((Second)other).z;
48        System.out.println("x = "+ this.x + " y = "+ this.y + " z = "+ this.z);
49    }
50}
51
52public class Tester {
53    public static void main(String[] args) {
54        First f1 = new First (40);
55        First f2 = new First (40, 50);
56        First f3 = new Second (100);
57        Second s1 = new Second (100);
58        Second s2 = new Second (100);
59        //***
60    }
61}