Courses/Mathesis/Intro2ProgrammingWithJava/Week4/4.2-Polymorphism/sandbox/shape.html

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<sandbox version="java17" mainclass="Main" preview="true" v-cloak>
<sandbox-source name="Main.java">
record Point(int x, int y) {}

interface IShape {
    double area();
    double perimeter();
    void draw();
} 

abstract class Shape implements IShape  {   
    protected final Point[] points;

    Shape(int edges) {
        this.points = new Point[edges];
        draw(); // (2)
    }

    Shape(Point[] points) {
        this.points = points;
    }

    public int getEdges() {
        return this.points.length;
    }
    
    @Override
    public void draw() {
        System.out.println("Draws a shape...");
    }
}

class Rectangle extends Shape {

    private final int width, height;

    Rectangle(int width, int height) {
        super(4);
        this.width = width;
        this.height = height;
    }

    Rectangle(Point[] points, int width, int height) {
        super(points);
        this.width = width;
        this.height = height;
    }

    public int getWidth() {
        return width;
    }

    public int getHeight() {
        return height;
    }

    @Override
    public double area() {
        return width * height;
    }

    @Override
    public double perimeter() {
        return 2 * width + 2 * height;
    }
    
    @Override
    public void draw() {
        System.out.println("Draws a rectangle...");
    }    
}

class Circle extends Shape {

    private final int radius;

    Circle() {
        super(1);	// (1)
        this.radius = 1;
    }

    Circle(Point[] points, int radius) {
        super(points);
        this.radius = radius;
    }

    public int getRadius() {
        return radius;
    }

    @Override
    public double area() {
        return Math.PI * (radius * radius);
    }

    @Override
    public double perimeter() {
        return Math.PI * 2 * radius;
    }

    @Override
    public void draw() {
        System.out.println("Draws a circle...");	// (3)
    }
}

class Triangle extends Shape {

    Triangle(Point... points) {
        super(points);
    }

    public Point[] getPoints() {
        return points;
    }
    
    // see https://tinyurl.com/msfdtjme
    private double length(Point p1, Point p2) {
        return Math.sqrt((p2.x() - p1.x()) * (p2.x() - p1.x()) + (p2.y() - p1.y()) * (p2.y() - p1.y()));
    }
    
    // see https://www.ypologismos.gr/emvadon-trigonou-xerontas-3-pleyres-typos-hrona/
    @Override
    public double area() {
        double s = perimeter()/2;
        double a = length(points[0], points[1]);
        double b = length(points[1], points[2]);
        double c = length(points[2], points[0]);
        return Math.sqrt(s*(s-a)*(s-b)*(s-c));
    }

    // https://www.ypologismos.gr/emvadon-trigonou-xerontas-3-pleyres-typos-hrona/
    @Override
    public double perimeter() {
        return length(points[0], points[1]) + length(points[1], points[2]) + length(points[2], points[0]);
    }
	
    @Override
    public void draw() {
        System.out.println("Draws a triangle...");	// (3)
    }	
}

public class Main {  
  public static void main(String[] args) {
	Point[] points = new Point[1];
	points[0] = new Point(10, 10);
	Shape c = new Circle(points, 10);
	System.out.println(c.perimeter());
	System.out.println(c.area());
	c.draw();
	
	points = new Point[1];
	points[0] = new Point(0, 0);
	Shape r = new Rectangle(points, 10, 10);
	System.out.println(r.perimeter());
	System.out.println(r.area());
	r.draw();	
	
	points = new Point[3];
	points[0] = new Point(0, 0);
	points[1] = new Point(10, 10);
	points[2] = new Point(-10, -10);	
	Shape t = new Triangle(points);
	System.out.println(t.perimeter());
	System.out.println(t.area());
	t.draw();	
  }
}
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