take screenshot using java

Rectangle screenRect = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize());
BufferedImage captureImage = new Robot().createScreenCapture(screenRect);
ImageIO.write(captureImage, "png", new File("/screenshot.png"));

In one line:

BufferedImage captureImage = new Robot().createScreenCapture(new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()));
ImageIO.write(captureImage, "png", new File("/screenshot.png"));