Currently, you have something like:

1. if (xpos >= width) {
2. xpos = 0;
3. // clear the screen by resetting the background:
4. background(0);
5. } else {
6. // increment the horizontal position for the next reading:
7. line(xpos, height, xpos, height - (int)this.arraySerial[0]);
8. xpos++;
9. }

with draw() acting as a loop.
If you want to draw your data at once, you have to make the loop explicit:

1. // clear the screen by resetting the background:
2. background(0);
3. for (int xpos = 0; xpos < width; xpos++) {
4. // increment the horizontal position for the next reading:
5. line(xpos, height, xpos, height - (int) arraySerial[0]);
6. }

And, as said, width must be equal to arraySerial.length (to avoid going beyond the bounds of the array).

Thanks for your reply. 

See http://processing.org/reference/
width and height are predefined variables, holding indeed the size defined by the size() call.