Exercise: Creating circles

Exercise: Circle - Part I

Point

  • contains x and y

  • copy Point.java

class Point {
    private double x, y;

    //=== constructors ===

    //default constructor
    Point() {
        x =0;
        y = 0;
    }

    Point(double new_x, double y) {
        x = new_x;
        this.y = y;
    }

    //copy constructor
    Point(Point p) {
        x = p.x; // Since this is the same class I can access without getter/setter
        y = p.y;
    }

    //=== static methods ===
    public static double distance(Point a, Point b) {
        double dist = Math.pow(a.x-b.x, 2) + Math.pow(a.y-b.y, 2);
        return Math.sqrt(dist);
    }

    //=== getters and setters ===
    public double getX() {
        return x;
    }

    public void setX(double x) {
        this.x = x;
    }

    public double getY() {
        return y;
    }

    public void setY(double y) {
        this.y = y;
    }

    public String toString() {
        return "Point {" + " x=" + x + ", y=" + y + " }";
    }
}

Write the following class:

  • Circle

    • contains a point and radius

the Circle class should include the following functions (methods):

  • 3 constructors

    • default constructor

    • copy constructor

    • Circle(double x, double y, double radius)

  • getters and setters (for point and radius)

  • public static boolean intersect(Circle a, Circle b)

  • public double circumference ()

  • public double area()

  • toString()

Solution

public class Main {
    public static void main(String[] args) {
        Circle circle1 = new Circle(0, 3, 5);
        Circle circle2 = new Circle(0, 12.9, 5);

        System.out.println(circle1);
        System.out.println(circle2.toString()); //same as System.out.println(circle2)

        boolean doesIntersect = Circle.intersect(circle1, circle2);
        System.out.println("Intersects? " + doesIntersect);

        System.out.println("Area of circle1: " + circle1.circumference() );
    }
}
Circle { Point { x=0.0, y=3.0 }, radius=5.0 }
Circle { Point { x=0.0, y=12.9 }, radius=5.0 }
Intersects? true
Area of circle1: 31.41592653589793

Exercise: Circle - Part II - adding intersections and random circles

add the following functions to Circle

  • intersect - return if 2 circles intersect

  • intersections - print all the circles that intersect

  • createRandomCircles - generate x amount of random circles

class Circle {
    //add before

    //=== static methods ===
    public static boolean intersect(Circle a, Circle b) {
        //your code
    }


    public static void intersections(Circle[] circles) {
       //your code
    }

    public static Circle[] createRandomCircles(int amount){
        //your code
    }
}



public class Main {
    public static void main(String[] args) {
        //Circle[] circles = new Circle[]{ new Circle(0, 3, 5), new Circle(0, 13, 5)};
        Circle[] circles = Circle.createRandomCircles(10);

        Circle.intersections(circles);
    }
}

Solution

class Circle {
    //add before

    //=== static methods ===
    public static boolean intersect(Circle a, Circle b) {
        double distance =  Point.distance(a.point, b.point);
        return (distance <= a.radius + b.radius);
    }


    public static void intersections(Circle[] circles) {
        boolean[][] checked = new boolean[circles.length][circles.length]; //default is false

        for (int i = 0; i < circles.length; i++) 
            for (int j = 0; j < circles.length; j++) 
                if (i!=j && !(checked[i][j]) && intersect(circles[i], circles[j])){
                    System.out.println(circles[i] + " and " + circles[j] + " intersect");
                    checked[i][j] = true;
                    checked[j][i] = true;
                }
    }

    public static Circle[] createRandomCircles(int amount){
        Circle[] circles = new Circle[amount];
        int min_point = -30;
        int max_point =  30;
        int min_radius = 2;
        int max_radius = 5;

        for (int i = 0; i < circles.length; i++) {
            double x = (int) ((Math.random() * ((max_point+1) - min_point)) + min_point);
            double y = (int) ((Math.random() * ((max_point+1) - min_point)) + min_point);
            double radius = (int) ((Math.random() * ((max_radius+1) - min_radius)) + min_radius);
            circles[i] = new Circle(x, y, radius);
        }

        return circles;
    }
}

Exercise: Circle - Part III - drawing circles with StdDraw

add the following functions to Circle

  • draw - draw the circle (non static)

  • setWindowForCircles - set the window size, find: min of x, min of y, max of x and max of y

    • find the 4 edges of the window

    • Then use StdDraw.setXscale() and StdDraw.setYscale()

import java.awt.Color;
import java.awt.Font;

class Circle {
    //add before ...
    public static void setWindowForCircles(Circle[] circles){
        //your code

        //fill in the functions: 
        // StdDraw.setXscale();
        // StdDraw.setYscale();
    }

   public void draw() {
        //your code
    }
}
public class Main {
    public static void main(String[] args) {
        Circle[] circles = Circle.createRandomCircles(10);

        Circle.setWindowForCircles(circles);
        Circle.intersections(circles);

        for (int i = 0; i < circles.length; i++){
            circles[i].draw();
//            System.out.println(circles[i]);
        }
    }
}

Solution

public class Main {
    public static void main(String[] args) {
        Circle[] circles = Circle.createRandomCircles(10);

        Circle.setWindowForCircles(circles);
        Circle.intersections(circles);

        for (int i = 0; i < circles.length; i++){
            circles[i].draw();
//            System.out.println(circles[i]);
        }
    }
}

Circle { Point { x=29.0, y=17.0 }, radius=4.0 } and Circle { Point { x=27.0, y=16.0 }, radius=2.0 } intersect

Code until now

To make the circles move we add some dx and dy to their position, also we can increase and decrease their size. We also have to in account the boundary of the window.

public class Main {
    public static void main(String[] args) {
        Circle[] circles = Circle.createRandomCircles(10);
        Circle.setWindowForCircles(circles);

        Circle.intersections(circles);

        for (int i = 0; i < circles.length; i++){
            circles[i].draw();
//            System.out.println(circles[i]);
        }
    }
}
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