DrawPolygon

import javax.swing.JFrame;
import javax.swing.JPanel;

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Polygon;

public class DrawPolygon extends JFrame {
    public DrawPolygon() {
        add(new PolygonPanel());
    }
    
    /** Main method */
    public static void main(String[] args) {
        DrawPolygon frame = new DrawPolygon();
        frame.setTitle("DrawPolygon");
        frame.setSize(300, 200);
        frame.setLocationRelativeTo(null); //Center the frame
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }
}

//Draw a polygon in the panel
class PolygonPanel extends JPanel {
    protected void paintComponent(Graphics g) {
        int xCenter = getWidth() / 2;
        int yCenter = getHeight() / 2;
        int radius = Math.min(getWidth(), getHeight()) / 2;
        
        int[] xPoints = new int[6];
        int[] yPoints = new int[6];
        int nPoints = 6;
        
        for(int i = 0; i < nPoints; i++) {
            xPoints[i] = (int)(xCenter + radius * Math.cos(Math.PI / 3 * i));
            yPoints[i] = (int)(yCenter + radius * Math.sin(Math.PI / 3 * i));
        }
        
        // Create a Polygon object
        Polygon polygon = new Polygon(xPoints, yPoints, nPoints);
        
        super.paintComponent(g);
        
        // Draw the polygon
        g.setColor(Color.RED);
        g.drawPolygon(polygon);
    }
}