1. class LineFile {
2.   ArrayList myLines;
3.   LineFile( String filename ){
4.     myLines = new ArrayList();
5.     String[] fileContents = loadStrings( filename );
6.     for( int i=0; i < fileContents.length; i++ ){
7.       String[] lineContents = fileContents[i].split(" ");
8.       if( lineContents[0].equals("draw") ){
9.         boolean fx=false, fy=false;
10.         int x=0,y=0;
11.         for( int j = 1; j < lineContents.length; j++ ){
12.           if( lineContents[j].length() > 0 && lineContents[j].charAt(0) == 'X' ){
13.             fx = true;
14.             x = int( lineContents[j].substring(1,lineContents[j].length()) );
15.           } else if( lineContents[j].length() > 0 && lineContents[j].charAt(0) == 'Y' ){
16.             fy = true;
17.             y = int( lineContents[j].substring(1,lineContents[j].length()) );
18.           }
19.           if( fx && fy ){
20.             myLines.add( new PVector( x, y, 0 ) );
21.             //println( x + " " + y );
22.           }
23.         }
24.       }
25.     }
26.   }
27.   void render(){
28.     int x=0,y=0;
29.     for( int i=0; i < myLines.size(); i++ ){
30.       PVector pv = (PVector) myLines.get(i);
31.       line( x, y, x+pv.x, y+pv.y);
32.       x+=pv.x;
33.       y+=pv.y;
34.     }
35.   }
36. }
37. 
    
38. LineFile myFile;
39. 
    
40. void setup(){
41.   myFile = new LineFile( "lineslist.txt" );
42.   size(200,200);
43. }
44. 
    
45. void draw(){
46.   background(255);
47.   stroke(0);
48.   myFile.render();
49. }

LineFile myFile;
boolean isLoaded;

void setup(){
  //myFile = new LineFile( "lineslist.txt" );
  isLoaded = false;
  size(200,200);
}

void draw(){
  background(255);
  stroke(0);

This is correct, at least as far as I am concerned.
You see, the parser I wrote doesn't use the data in the file as points in space, but as directions on which way to go next.

I wrote it this way for three reasons:

1) You didn't specify how you wanted the data to be used to draw lines.
2) This is a more natural interpretation of the data the way it was presented. Usually a line is defined by 4 values: two for a starting point (x,y), and two more for an ending point (x',y'). Since your data one has enough data for a single point, I instead decided to use them as directions.
3) I'm evil. I realized that this was not what you wanted and anticipated that you would need to fix this. This would get you to look at my posted code in more detail and thus you would actually have to learn something and do some work.

If you want to do a square:

draw X10 Y0

draw X0 Y10
draw X-10 Y0

draw X0 Y-10