package pattpack.image;

import java.util.Hashtable;

/**
 * This class creates instances of classes that
 * read images in specific formats, e.g., gif, jpeg, png, ...
 * It does not need to be public.  It is public to ease the documentation.
 */

public class ImageReaderFactory {
    /**
     *  Maps filename extensions, e.g., "gif", "jpg",
     *  to classes, e.g., pattpack.image.GifReader.class.
     */
    private static Hashtable classes = new Hashtable();

    /**
     *  Singleton class.
     */
    private ImageReaderFactory () {}
    
    /** Fill the hashtable. */
    static {
        classes.put("gif", pattpack.image.GifReader.class);
        classes.put("jpg", pattpack.image.JpegReader.class);
        classes.put("png", pattpack.image.PngReader.class);
        //...
    }
    /**
     * Create an ImageReader object to read an image in a specified format.
     * @param format The extension of the filename containing the image.
     * @return An instance of a class that reads images in a particular
     *         format, or null if the format is not understood.
     */
    public static ImageReader createImageReader (String format) {
        Class myClass = (Class) classes.get (format);
        try {
            return (ImageReader) myClass.newInstance ();
        } catch (Exception e) {
	    System.err.println ("Unknown format "+format);
            return null;
        }
    }     
}