GraphicsDevice[] screens = GraphicsEnvironment.getLocalGraphicsEnvironment().getScreenDevices();  //same screens[] with JRE7 and JRE8

Robot rbt0 = new Robot(screens[0]);
BufferedImage image0 = rbt0.createScreenCapture(new Rectangle(0,0,1024,1024));

Robot rbt1 = new Robot(screens[1]);
BufferedImage image1 = rbt1.createScreenCapture(new Rectangle(0,0,1024,1024));

Robot rbt1 = new Robot(screens[1]);
BufferedImage image1 = rbt1.createScreenCapture(new Rectangle(1024,0,1024,1024));