openclose.java

import java.util.*;

interface Shape{
    double getArea();
}

class Circle implements Shape{
    double radius;
    Circle(double radius){
        this.radius = radius;
    }
    public double getArea(){
        return Math.PI*this.radius*this.radius;
    }
}

class Square implements Shape{
    double side;
    Square(double side){
        this.side = side;
    }
    public double getArea(){
        return side*side;
    }
}
class Rectangle implements Shape{
    double length,width;
    Rectangle(double x,  double y){
        this.length = x;
        this.width=y;
    }
    public double getArea(){
        return length*width;
    }
}
class CalculateAreaSummation{
    ArrayList<Shape>arr = new ArrayList<>();
    double total = 0;

    void addShape(Shape shape){
        arr.add(shape);
    }

    public double calcArea(){
        this.total = 0;
        for(Shape shape : arr){
         total+=shape.getArea();
        }
        return total;
    }

    void printOutput(){
        System.out.println("total: " + total);
    }
}


class OpenClosed{
    public static void main(String[] args){
        Shape circle = new Circle(5);
        Shape square = new Square(10);

        CalculateAreaSummation sum = new CalculateAreaSummation();
        sum.addShape(circle);
        System.out.println(sum.calcArea());

        sum.addShape(square);
        System.out.println(sum.calcArea());
    }
}