Chapter 13 Exercise 11, Introduction to Java Programming, Tenth Edition Y. Daniel LiangY.

13.11 (The Octagon class)
Write a class named Octagon that extends GeometricObject and implements
the Comparable and Cloneable inter- faces. Assume that all eight sides
of the octagon are of equal length. The area can be computed using the
following formula:
area = (2 + 4/22)* side * side
Draw the UML diagram that involves Octagon, GeometricObject, Comparable, and Cloneable.
Write a test program that creates an Octagon object with side value 5
and displays its area and perimeter. Create a new object using the clone method
and compare the two objects using the compareTo method.

public class Octagon extends GeometricObject implements Cloneable {

    // all 8 sides of the octagon have equal length
    double side;


    public Octagon() {
        this(5);
    }

    public Octagon(double side) {
        this.side = side;
    }

    @Override
    public double getArea() {
        return (2.0 + 4.0 / Math.sqrt(2) * side * side);
    }

    @Override
    public double getPerimeter() {
        return side * 8;
    }

    public Object clone() {
        Object o = null;
        try {
            o = super.clone();
        } catch (CloneNotSupportedException ex) {
            ex.printStackTrace();
        }
        return o;
    }

    @Override
    public boolean equals(Object o) {
        return o instanceof Octagon && getArea() == ((Octagon)o).getArea();
    }
}

public class Exercise_11 {

    public static void main(String[] args) {
        Octagon oc1 = new Octagon(10);
        Octagon oc2 = (Octagon)oc1.clone();

        System.out.println("compareTo: " + (oc1.compareTo(oc2) == 0));
        System.out.println("equals: " + oc1.equals(oc2));
        System.out.println("Have the same reference? " + (oc1 == oc2));
    }
}