PLabel label;
PScrollBar scrollbar;

int value;

void setup() {
  label = new PLabel("Value: " + value);
  label.align = CENTER;
  label.calculateBounds(4, 4, width - 8, height);
  label.setBounds(4, 4, width - 8, label.height);
  label.initialize();
  
  int y = label.y + label.height + 4;
  scrollbar = new PScrollBar();
  scrollbar.setBounds((width - 4) / 2, y, 4, height - y - 4);
  scrollbar.setRange(0, 8, 1);
  scrollbar.initialize();  
}

void draw() {
  background(255);
  label.draw();
  scrollbar.draw();
}

void keyPressed() {
  switch (keyCode) {
    case UP:
      value = max(0, value - 1);
      break;
    case DOWN:
      value = min(8, value + 1);
      break;
  }
  label.text = "Value: " + value;
  scrollbar.setValue(value);
}