int x1 = 10;
int y1 = 40;
int w1 = 280;
int h1 = 120;
boolean m1 = false;  //whether box 1 moves
int i1 = 1;          //increment value when moving box1

int x2 = 10;
int y2 = 60;
int w2 = 40;
int h2 = 80;
boolean m2 = false;  //whether box 2 moves
int i2 = 1;          //increment value when moving box2

int x3 = 10;
int y3 = 74;
int w3 = 10;
int h3 = 52;
boolean m3 = true;  //whether box 3 moves
int i3 = 2;         //increment value when moving box3

void setup() {
  size(300, 200);
  framerate(60);
}

void draw() {
  background(255, 255, 255);
  stroke(0, 0, 0);
  rect(x1, y1, w1, h1);
  rect(x2, y2, w2, h2);
  rect(x3, y3, w3, h3);
  if(m3 && (x3 + w3 < x2 + w2)) //box3 can move and has not run into box2's right side
  {
    x3 = x3 + i3;
  } else if(m3 && !(x3 + w3 < x2 + w2)) //box3 can move and has run into box2's right side
  {
    m3 = false;
    m2 = true;
  }
  if((m2 && (x2 + w2 < x1 + w1)) //box2 can move and has not run into box1's right side
  && (m2 && (x2 < x3 ))) //box2 can move and has not run into box3's left side
  {
    x2 = x2 + i2;
  } else if(m2 && !(x2 < x3)) { //box2 can move and has run into box3's left side
    m2 = false;
    m3 = true;
  }
  
}