You want to make a bitmap of screen ?

if yes, then try this code.
Toolkit toolkit = Toolkit.getDefaultToolkit();
Dimension screenSize = toolkit.getScreenSize();
Rectangle screenRect = new Rectangle(screenSize);
// create screen shot
Robot robot = new Robot();
BufferedImage image  = robot.createScreenCapture
(screenRect);
// save captured image to PNG file
String imageFileName = File.separatorChar
+ "Automation" + File.separatorChar + outFileName ;
ImageIO.write(image, "png", new File(imageFileName));
// give feedback

Intereting, I never knew about that class(Robot). Does it do the
actions on screen or just in the memory?

Action on screen. It works same way as "PrtSc" works. There should
be one button on your comp says "Print Screen" or "PrtSc" press that
key and open the paint and past it there. the output you there is
same think this code does.