gistfile1.java

private Icon[] icons = new Icon[2];
private int iconIndex = 0;

registerIcons()
{
  icons[0] = register.registerblahblah
  icons[1] = register.registerblahblahsomethingdifferent
}

getIcon()
{
return icons[iconIndex];
}

onBlockActivated()
{
iconIndex = iconIndex == 0 ? 1 : 0;
}