This example uses java.awt.Robot class to capture the screen pixels and returns a BufferedImage. Java.awt.Robot class is used to take the control of mouse and keyboard. Once you get the control, you can do any type of operation related to mouse and keyboard through your java code. This class is used generally for test automation.
Copy and paste following code in your Java class and invoke the method captureScreen() with file name as argument. The screen shot will be stored in the file that you specified in argument.