jButton1.addMouseListener(new java.awt.event.MouseAdapter() {
    public void mouseEntered(java.awt.event.MouseEvent evt) {
        jButton1.setBackground(Color.GREEN);
    }
    public void mouseExited(java.awt.event.MouseEvent evt) {
        jButton1.setBackground(UIManager.getColor("control"));
    }
});

jButton1.addMouseListener(new java.awt.event.MouseAdapter() {
    Font originalFont = null;
 
    public void mouseEntered(java.awt.event.MouseEvent evt) {
        originalFont = jButton1.getFont();
        Map attributes = originalFont.getAttributes();
        attributes.put(TextAttribute.UNDERLINE, TextAttribute.UNDERLINE_ON);
        jButton1.setFont(originalFont.deriveFont(attributes));
    }
 
    public void mouseExited(java.awt.event.MouseEvent evt) {
        jButton1.setFont(originalFont);
    }
});