OpenGL question

 
import java.awt.*;
import javax.swing.*;
import javax.media.opengl.*;
 
public class ductranhw1 extends J1_0_Point {
 
    double centerX = WIDTH / 2, centerY = HEIGHT / 2, radius = WIDTH / 3, theta = 0;
    double delta = 4 / (Math.PI * radius);
 
    public ductranhw1() {
        capabilities.setDoubleBuffered(true);
    }
 
    public void display(GLAutoDrawable drawable) {
 
        GL gl = drawable.getGL();
        gl.glClear(GL.GL_COLOR_BUFFER_BIT);
 
        // draw circle
        gl.glColor3f(1.0f, 1.0f, 1.0f);
        gl.glPointSize(4);
        drawCircle(centerX, centerY, radius);
 
        for (int i = 0; i < 50; i++) {
            //draw red point
            theta = theta + delta;
            double x = radius * Math.cos(theta) + centerX;
            double y = radius * Math.sin(theta) + centerY;
            gl.glPointSize(10);
            gl.glColor3f(1.0f, 0.0f, 0.0f);
 
            try {
                drawPoint(x, y);
                Thread.sleep(10);
 
            } catch (Exception ignore) {
            }
        }
    }
 
    public static void main(String[] args) {
        ductranhw1 frame = new ductranhw1();
        frame.setTitle("Duc Tran Minh Homework1");
        frame.setSize(WIDTH, HEIGHT);
        frame.setVisible(true);
    }
 
    private void drawCircle(double centerX, double centerY, double radius) {
        double th = 0;
        while (th <= 2 * Math.PI) {
            th = th + delta;
            double x = radius * Math.cos(th) + centerX;
            double y = radius * Math.sin(th) + centerY;
            drawPoint(x, y);
        }
    }
 
    private void drawPoint(double x, double y) {
        gl.glBegin(GL.GL_POINTS);
        gl.glVertex2d(x, y);
        gl.glEnd();
    }
}