java - getWidth not working correctly as class variable -

i new java (and programming in general) , trying make program draws vertical line down centre of screen. this, made variable x gives me x coordinate of centre of screen. wanted able use variable within other private methods. when run code however, no line appears, if x set 0.

import acm.graphics.*; import acm.program.*; import java.awt.*;  public class target extends graphicsprogram {        int x = getwidth()/2;     public void run() {         gline line = new gline (x,0,x,300);         add (line);     } } 

if put variable x inside run() method below, line drawn correctly, not able use later in other private methods understanding variable no longer class variable instance variable , therefor accessible run() , no other methods?

public class target extends graphicsprogram {       public void run() {         int x = getwidth()/2;                     gline line = new gline (x,0,x,300);         add (line);     } } 

could enlighten me why first code not work whereas second 1 does? thank in advance!

in first version getwidth() called during instance initialisation , bounds of window has not been set yet. still works method returns 0 , don't see line on screen.