public class ImageReaderFactory {
    static ImageReader reader;

    public static ImageReader getImageReader (ImageTypes type) {

            if (type.equals(ImageTypes.BMP)) {
                reader = new BmpReader();
            } else if (type.equals(ImageTypes.PNG)) {
                reader = new PngReader();
            } else if (type.equals(ImageTypes.JPG)) {
                reader = new JpgReader();
            } else if (type.equals(null)) {
                throw new NullPointerException("NullPointerException(\"Unbekannter Bildtyp\").");
            } else {
                throw new IllegalArgumentException ("IllegalArgumentException(\"Unbekannter Bildtyp\").");
        }
        return reader;
    }
}
Vielen lieben Dank :-)