Steps to reproduce:

- Install Ubuntu 14.04 on VirtualBox
- Install VirtualBox Guest Additions
- Install JDK 9
- Run the program:
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import java.io.File;
import javax.imageio.ImageIO;
import java.awt.Dimension;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;

public class ScreenCaptureTest {

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

        if (args.length < 1) {
            throw new RuntimeException("Image save path is not specified!");
        }

        Robot robot = new Robot();
        Dimension screenSize = Toolkit.getDefaultToolkit().getScreenSize();
        BufferedImage image = robot.createScreenCapture(new Rectangle(screenSize));
        ImageIO.write(image, "png", new File(args[0], "screenshot.png"));
    }
}
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The saved image is either black or only desktop background is saved.