// relevant includes go here ...

public class DrawTransparentText {
   // the composite generation function
   // this simply tells Java2d how transparent
   // the render of the subsequent drawing calls
   // should be
   private AlphaComposite makeComposite(float alpha) {
       int type = AlphaComposite.SRC_OVER;
       return(AlphaComposite.getInstance(type, alpha));
   }
   // random "timer" variable
   private float   m_fade = 3.0f;   

   public void drawText(Graphics2D g2d, String text, /* other stuff ... */) {
       // again, you need to save the old composite value
       // because you have to reset it, otherwise
       // all drawing operations to this graphics context
       // will be transparent (which is bad ..)
       Composite saved = g2d.getComposite();
       // just an example ...
       g2d.setComposite(makeComposite(m_fade * 0.1f);
       // set up the color, font, ect
       // the color is now transparent 
       // (with the selected alpha value)
       g2d.setColor( ... );
       // draw the string
       g2d.drawString( ... );
       // reset the composite
       g2d.setComposite(saved);
   }
}