Draw a circle with a radius and points around the edge

Question

I'm really stuck on how to go about programming this. How to draw a circle in Java with a radius and points around the edge?

I need to draw a circle within a JFrame with a radius and points around the circumference. i can mathematically calculate how to find the coordinates of the point around the edge but i cant seem to be able to program the circle. I am currently using a Ellipse2D method but that doesn't seem to work and doesn't return a radius, as under my understanding, it doesn't draw the circle from the center rather from a starting coordinate using a height and width.

My current code is on a separate frame but I need to add it to my existing frame.

import java.awt.*;  import javax.swing.*;  import java.awt.geom.*;   public class circle extends JFrame {    public circle() {       super("circle");       setSize(410, 435);       setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);       Panel sp = new Panel();       Container content = getContentPane();       content.add(sp);       setContentPane(content);       setVisible(true);   }    public static void main (String args[]){   circle sign = new circle();   }  }   class Panel extends JPanel {   public void paintComponent(Graphics comp) {       super.paintComponent(comp);       Graphics2D comp2D = (Graphics2D) comp;        comp2D.setColor(Color.red);       Ellipse2D.Float sign1 = new Ellipse2D.Float(0F, 0F, 350F, 350F);       comp2D.fill(sign1);   }  } 

Answer 1

Points on a circle may be specified as a function of the angle θ:

x = a + r cos(θ)
y = b + r sin(θ)

Here, increments of 2π/8 are shown.

Addendum: As suggested in a comment by @Christoffer Hammarström, this revised example reduces the number of magic numbers in the original. The desired number of points becomes a parameter to the constructor. It also adapts the rendering to the container's size.

/** @see https://stackoverflow.com/questions/2508704 */ public class CircleTest extends JPanel {      private static final int SIZE = 256;     private int a = SIZE / 2;     private int b = a;     private int r = 4 * SIZE / 5;     private int n;      /** @param n  the desired number of circles. */     public CircleTest(int n) {         super(true);         this.setPreferredSize(new Dimension(SIZE, SIZE));         this.n = n;     }      @Override     protected void paintComponent(Graphics g) {         super.paintComponent(g);         Graphics2D g2d = (Graphics2D) g;         g2d.setRenderingHint(             RenderingHints.KEY_ANTIALIASING,             RenderingHints.VALUE_ANTIALIAS_ON);         g2d.setColor(Color.black);         a = getWidth() / 2;         b = getHeight() / 2;         int m = Math.min(a, b);         r = 4 * m / 5;         int r2 = Math.abs(m - r) / 2;         g2d.drawOval(a - r, b - r, 2 * r, 2 * r);         g2d.setColor(Color.blue);         for (int i = 0; i < n; i++) {             double t = 2 * Math.PI * i / n;             int x = (int) Math.round(a + r * Math.cos(t));             int y = (int) Math.round(b + r * Math.sin(t));             g2d.fillOval(x - r2, y - r2, 2 * r2, 2 * r2);         }     }      private static void create() {         JFrame f = new JFrame();         f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         f.add(new CircleTest(9));         f.pack();         f.setVisible(true);     }      public static void main(String[] args) {         EventQueue.invokeLater(new Runnable() {              @Override             public void run() {                 create();             }         });     } }