Botones de diferente forma

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.GradientPaint;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Polygon;
import java.awt.Rectangle;
import java.awt.Shape;
import java.awt.geom.RoundRectangle2D;
 
import javax.swing.AbstractButton;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.plaf.basic.BasicButtonUI;
 
public class ShapedButton {
 
 private static JFrame frame;
 
 public Component createComponents() {
 
  // Tres botones para probar diferentes efectos
  JButton roundButton = new JButton("Redondo");
  JButton squareButton = new JButton("Cuadrado");
  JButton polygonButton = new JButton("Poligonal");
 
  // Establecemos un UI específico
  ShapedButtonUI roundUI = new ShapedButtonUI();
  roundUI.setShape(ButtonShape.ROUND, roundButton);
  roundButton.setUI(roundUI);
  roundButton.setPreferredSize(new Dimension(100, 100));
  ShapedButtonUI squareUI = new ShapedButtonUI();
  squareUI.setShape(ButtonShape.SQUARE, squareButton);
  squareButton.setUI(squareUI);
  squareButton.setPreferredSize(new Dimension(100, 100));
  ShapedButtonUI polygonUI = new ShapedButtonUI();
  polygonUI.setShape(ButtonShape.POLYGON, polygonButton);
  polygonButton.setUI(polygonUI);
  polygonButton.setPreferredSize(new Dimension(100, 100));
 
  // Añadimos nuestros componentes
  JPanel panel = new JPanel();
  panel.add(roundButton);
  panel.add(squareButton);
  panel.add(polygonButton);
 
  return panel;
 }
 
 /**
  * Definimos tres posibles formas para los botones
  */
 public enum ButtonShape {
  ROUND,
  SQUARE,
  POLYGON
 }
 
 private class ShapedButtonUI extends BasicButtonUI {
 
  /** Button shape. */
  private ButtonShape shape;
 
  public ShapedButtonUI() {
   super();
  }
 
  public void setShape(ButtonShape shape, JButton button){
   // no pintamos el borde
   button.setBorderPainted(false);
   this.shape = shape;
  }
 
  @Override
  public void paint(Graphics g, JComponent c) {
 
   Graphics2D g2d = (Graphics2D) g;
 
   // definamos las formas de nuestros botones
   Shape buttonShape = null;
   switch (shape) {
    case ROUND:
     buttonShape = new RoundRectangle2D.Double(0, 0, c.getWidth() - 1, c.getHeight() - 1, 50, 50);
     break;
    case SQUARE:
     buttonShape = new Rectangle(0, 0, c.getWidth(), c.getHeight());
     break;
    case POLYGON:
     int[] xPoints = {0, 0 + c.getWidth() / 3, 0 + 2 * (c.getWidth() / 3), c.getWidth(), 0 + 2 * (c.getWidth() / 3), 0 + c.getWidth() / 3};
     int[] yPoints = {c.getHeight() / 2, 0, 0, c.getHeight() / 2, c.getHeight(), c.getHeight()};
     buttonShape = new Polygon(xPoints, yPoints, 6);
     break;
   }
 
   // establecemos un gradiente para el fondo del boton
   GradientPaint gp = new GradientPaint(0, 0, Color.GREEN, c.getWidth(), c.getHeight(), Color.BLUE);
   g2d.setPaint(gp);
   g2d.fill(buttonShape);
 
   super.paint(g2d, c);
 
  }
 
  @Override
  protected void paintButtonPressed(Graphics g, AbstractButton b) {
   Graphics2D g2d = (Graphics2D) g;
 
   // definamos las formas de nuestros botones
   Shape buttonShape = null;
   switch (shape) {
    case ROUND:
     buttonShape = new RoundRectangle2D.Double(0, 0, b.getWidth() - 1, b.getHeight() - 1, 50, 50);
     break;
    case SQUARE:
     buttonShape = new Rectangle(0, 0, b.getWidth(), b.getHeight());
     break;
    case POLYGON:
     int[] xPoints = {0, 0 + b.getWidth() / 3, 0 + 2 * (b.getWidth() / 3), b.getWidth(), 0 + 2 * (b.getWidth() / 3), 0 + b.getWidth() / 3};
     int[] yPoints = {b.getHeight() / 2, 0, 0, b.getHeight() / 2, b.getHeight(), b.getHeight()};
     buttonShape = new Polygon(xPoints, yPoints, 6);
     break;
   }
 
   // establecemos un gradiente para el fondo del boton
   GradientPaint gp = new GradientPaint(0, 0, Color.BLUE, 0, b.getHeight(), Color.GREEN);
   g2d.setPaint(gp);
   g2d.fill(buttonShape);
  }
 }
 
 /**
  * Create the GUI and show it. For thread safety,
  * this method should be invoked from the
  * event dispatch thread.
  */
 private static void createAndShowGUI() {
 
  // Create and set up the window.
  frame = new JFrame("Shaped button");
  frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
  ShapedButton app = new ShapedButton();
  Component contents = app.createComponents();
  frame.getContentPane().add(contents, BorderLayout.CENTER);
 
  // Display the window.
  frame.pack();
  frame.setLocationByPlatform(true);
  frame.setVisible(true);
 }
 
 public static void main(String[] args) {
  // Schedule a job for the event dispatch thread:
  // creating and showing this application's GUI.
  javax.swing.SwingUtilities.invokeLater(new Runnable() {
   public void run() {
    createAndShowGUI();
   }
  });
 }
}