ניתוח ירושה והכלה במחלקות

1public class A {
2    public static int count = 0;
3    protected int num;
4
5    public A() {
6        this.num = 3;
7        count++;
8    }
9    public int getNum() {
10        return this.num;
11    }
12    public void setNum(int num) {
13        this.num = num;
14    }
15    public void foo(int num) {
16        this.num = num;
17        num++;
18    }
19    public boolean isEqual(A other) {
20        return (this.num == other.num);
21    }
22    public void func() {
23        System.out.println("I am A");
24    }
25}
26
27public class B extends A {
28    public void func() {
29        System.out.println("I am B");
30    }
31    public boolean isEqual(B other) {
32        return (this == other);
33    }
34}
35
36public class C extends A { }
37
38public class D {
39    private A a;
40
41    public D(A a) {
42        this.a = a;
43    }
44    public void func() {
45        (this.a).func();
46    }
47    public void isB() {
48        System.out.println((this.a) instanceof B);
49    }
50}