Probably not a bug, but: should we use the first (1x) file name _only_ to get the desired MultiResolutionImage? (is it specified somewhere?)

Please run the following test example:

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;
import sun.awt.image.MultiResolutionImage;

public class Test {

    private static final int IMAGE_WIDTH = 300;
    private static final int IMAGE_HEIGHT = 200;
    private static final Color COLOR_1X = Color.GREEN;
    private static final Color COLOR_2X = Color.BLUE;
    private static final String IMAGE_NAME_1X = "image.png";
    private static final String IMAGE_NAME_2X = "image@2x.png";

    public static void main(String[] args) throws Exception {

        generateImages();

        File imageFile = new File(IMAGE_NAME_1X); // ?
        String fileName = imageFile.getAbsolutePath();

        Image img = Toolkit.getDefaultToolkit().getImage(fileName);
        System.out.println("file: " + fileName);

        System.out.println("image class: " + img.getClass().getCanonicalName());
        MultiResolutionImage mri = (MultiResolutionImage) img;
    }

    static void generateImages() throws Exception {
        if (!new File(IMAGE_NAME_1X).exists()) { generateImage(1); }
        if (!new File(IMAGE_NAME_2X).exists()) { generateImage(2); }
    }

    static void generateImage(int scale) throws Exception {

        BufferedImage image = new BufferedImage(scale * IMAGE_WIDTH, scale * IMAGE_HEIGHT, BufferedImage.TYPE_INT_RGB);
        Graphics g = image.getGraphics();
        g.setColor(scale == 1 ? COLOR_1X : COLOR_2X);
        g.fillRect(0, 0, scale * IMAGE_WIDTH, scale * IMAGE_HEIGHT);
        File file = new File(scale == 1 ? IMAGE_NAME_1X : IMAGE_NAME_2X);
        ImageIO.write(image, "png", file);
    }
}

Output (Mac OS X 10.10.3, JDK9 b77) is as expected:
  file: /Users/xxx/work/tests/Test1/image.png
  image class: sun.awt.image.MultiResolutionToolkitImage

Then please replace "IMAGE_NAME_1X" with "IMAGE_NAME_2X" in line "File imageFile = ..."; the output will be:
  file: /Users/xxx/work/tests/Test1/image@2x.png
  image class: sun.awt.image.ToolkitImage
   Exception in thread "main" java.lang.ClassCastException: sun.awt.image.ToolkitImage cannot be cast to sun.awt.image.MultiResolutionImage
        at Test.main(Test.java:27)

is it an expected result?