This example is for Processing 3+. If you have a previous version, use the examples included with your software. If you see any errors or have suggestions, please let us know.

SaveFile 1

Saving files is a useful way to store data so it can be viewed after a program has stopped running. The saveStrings() function writes an array of strings to a file, with each string written to a new line. This file is saved to the sketch's folder.

int[] x = new int[0];
int[] y = new int[0];

void setup() 
  size(200, 200);

void draw() 
  for (int i = 0; i < x.length; i++) {
    vertex(x[i], y[i]);
  // Show the next segment to be added
  if (x.length >= 1) {
    line(mouseX, mouseY, x[x.length-1], y[x.length-1]);

void mousePressed() { // Click to add a line segment
  x = append(x, mouseX);
  y = append(y, mouseY);

void keyPressed() { // Press a key to save the data
  String[] lines = new String[x.length];
  for (int i = 0; i < x.length; i++) {
    lines[i] = x[i] + "\t" + y[i];
  saveStrings("lines.txt", lines);
  exit(); // Stop the program