Example: say you have an 'image' you want to scale you will need a bufferedImage probably, and probably will be starting out with just 'Image' object. So this works I think... The AVATAR_SIZE is the target width we want our image to be:
Image imgData = image.getScaledInstance(Constants.AVATAR_SIZE, -1, Image.SCALE_SMOOTH);
BufferedImage bufferedImage = new BufferedImage(imgData.getWidth(null), imgData.getHeight(null), BufferedImage.TYPE_INT_RGB);
bufferedImage.getGraphics().drawImage(imgData, 0, 0, null);