Android : How to take screenshoot or screen capture on android without root?

How to take screenshoot or screen capture on android without root ? 1. i have try this code :

 public void saveBitmap(Bitmap bitmap) {
             SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd_HHmmss");
             String currentDateandTime = sdf.format(new Date());

             sendBroadcast(new Intent(Intent.ACTION_MEDIA_MOUNTED, Uri.parse("file://"+ Environment.getExternalStorageDirectory())));
            File imagePath = new File(Environment.getExternalStorageDirectory() + currentDateandTime);
            FileOutputStream fos;
            try {
                fos = new FileOutputStream(imagePath);
                bitmap.compress(CompressFormat.PNG, 100, fos);
                fos.flush();
                fos.close();
            } catch (FileNotFoundException e) {
                Log.e("GREC", e.getMessage(), e);
            } catch (IOException e) {
                Log.e("GREC", e.getMessage(), e);
            }
        }   

but it's not working when i execute and i know thats because my phone not root. how to take screenshoot without root?