Hover Fade JButton -> http://pt.stackoverflow.com/questions/14059/efeito-na-borda-de-um-componente-jbutton

gistfile1.txt

package br;

import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.FlowLayout;
import javax.swing.*;
import javax.swing.JButton;
import javax.swing.JFrame;

public class CriarJButton extends JFrame {

    private static final long serialVersionUID = 1L;

    public CriarJButton() {
        this.getContentPane().setLayout(new FlowLayout());
        final botaoFade bt = new botaoFade("StackOverflow.pt");
        bt.addMouseListener(new java.awt.event.MouseAdapter() {
            public void mouseEntered(java.awt.event.MouseEvent evt) {
               bt.setAlpha((float)0.6);
            }
            public void mouseExited(java.awt.event.MouseEvent evt) {
                bt.setAlpha((float)1);
            }
        });
        add(bt);

    }

    private static void cria_MostraInterface() {

        JFrame painel = new CriarJButton();
        painel.pack();
        painel.setVisible(true);
        painel.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                cria_MostraInterface();
            }
        });
    }
    
    private static class botaoFade extends JButton {

        private static final JButton lafDeterminer = new JButton();
        private static final long serialVersionUID = 1L;
        private boolean rectangularLAF;
        private float alpha = 1f;

        botaoFade() {
            this(null, null);
        }

        botaoFade(String texto) {
            this(texto, null);
        }

        botaoFade(String texto, Icon icon) {
            super(texto, icon);
            setOpaque(false);
            setFocusPainted(false);
        }

        public float getAlpha() {
            return alpha;
        }

        public void setAlpha(float alpha) {
            this.alpha = alpha;
            repaint();
        }

        @Override
        public void paintComponent(java.awt.Graphics g) {
            java.awt.Graphics2D g2 = (java.awt.Graphics2D) g;
            g2.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha));
            if (rectangularLAF && isBackgroundSet()) {
                Color c = getBackground();
                g2.setColor(c);
                g.fillRect(0, 0, getWidth(), getHeight());
            }
            super.paintComponent(g2);
        }

        @Override
        public void updateUI() {
            super.updateUI();
            lafDeterminer.updateUI();
            rectangularLAF = lafDeterminer.isOpaque();
        }
    }
}