Używanie konstruktorów nad-klasy – super

package pl.am.object2.lesson30;

public class Dziedziczenie {

    public static void main(String[] args) {
        Prostokat prostokat = new Prostokat(2, 5);
        Kwadrat kwadrat = new Kwadrat(7);

        System.out.println(prostokat);
        System.out.println(kwadrat);
    }
}

package pl.am.object2.lesson30;

public class Kwadrat extends Prostokat {

    public Kwadrat(double bok) {
        super(bok, bok);
    }

    public double getBok() {
        return a;
    }

    @Override
    public String toString() {
        return "Kwadrat{" +
                "bok=" + a +
                ", pole=" + obliczPole() +
                ", obwód=" + obliczObwod() +
                '}';
    }
}

package pl.am.object2.lesson30;

public class Prostokat {
    protected final double a;
    protected final double b;

    public Prostokat(double a, double b) {
        this.a = a;
        this.b = b;
    }

    public double getA() {
        return a;
    }

    public double getB() {
        return b;
    }

    public double obliczPole() {
        return a * b;
    }

    public double obliczObwod() {
        return 2*a + 2*b;
    }

    @Override
    public String toString() {
        return "Prostokat{" +
                "a=" + a +
                ", b=" + b +
                ", pole=" + obliczPole() +
                ", obwód=" + obliczObwod() +
                '}';
    }
}