use a barcode scanner to store a barcode as a string in Processing

barcode.pde

String barcode = "";

void setup() {}

void draw() {}

void keyPressed() {
  barcode+=key;
  if (key == '\n') { // we've reached the end of the barcode
    println(barcode);
    barcode = ""; // reset the barcode to receive a new one
  }
}