I've been working on this all night. I have an array of 10 Rectangle objects. A rectangle has data values x,y,w,h which represent the X,Y location of the rectangle and it's height and width. no rectMode(); calls are used. I'm using this algorithm I found to try to detect collision between any of the 10 rects colliding as they move about:

1. boolean collDetect(Rectangle rect1, Rectangle rect2) { // this will be collison detection
   
     if (rect1.x+rect1.w < rect2.x) { return false; }
     if (rect1.x > rect2.x+rect2.w) { return false; }
     if (rect1.y+rect1.h < rect2.y) { return false; }
     if (rect1.y > rect2.y+rect2.h) { return false; }
   
   
     return true;     
   
   }

I loop through the objects like this in the draw() function:

1. for (int iii=0; iii <= 9; iii++) {
       for (int jjj=0; jjj<= 9; jjj++) {
         if (iii != jjj) { //not the same rect
           boolean coll = collDetect(myRects[iii],myRects[jjj]);
           if (coll == true) {
             myRects[iii].rectColor = color(255,0,0);
             myRects[jjj].rectColor = color(255,0,0);
           } else {
             myRects[iii].rectColor = color(0);
             myRects[jjj].rectColor = color(0);
           }
         }
       }
     }

To try to flag any collisions and turn the colliding rects red. But it only flags like 1/5 of all the collisons! Full source is below, see for yourself.

1. //TODO: Fix it so that they don't all fall into a state of just going one direc
   //TODO: do this by checking if movement is 0 on every boundry hit and reassign
   //TODO: if it is.
   
   final int windowSize = 500;
   
   
   Rectangle[] myRects;
   int locationX, locationY;
   
   
   void setup () {
     myRects = new Rectangle[10];
     for (int iii=0; iii <= 9; iii++) {
       locationX = int(random(windowSize));
       locationY = int(random(windowSize));
       myRects[iii] = new Rectangle(locationX, locationY);
     }
     size(windowSize,windowSize);
     noStroke();
   }
   
   void draw () {
     background(0,100,100);
     for (int iii=0; iii <= 9; iii++) {
       myRects[iii].update();
       for (int jjj=0; jjj<= 9; jjj++) {
         if (iii != jjj) { //not the same rect
           boolean coll = collDetect(myRects[iii],myRects[jjj]);
           if (coll == true) {
             myRects[iii].rectColor = color(255,0,0);
             myRects[jjj].rectColor = color(255,0,0);
           } else {
             myRects[iii].rectColor = color(0);
             myRects[jjj].rectColor = color(0);
           }
         }
       }
     }
   }
   
   boolean collDetect(Rectangle rect1, Rectangle rect2) { // this will be collison detection
   
     if (rect1.x+rect1.w < rect2.x) { return false; }
     if (rect1.x > rect2.x+rect2.w) { return false; }
     if (rect1.y+rect1.h < rect2.y) { return false; }
     if (rect1.y > rect2.y+rect2.h) { return false; }
   
   
     return true;     
   }
   
   class Rectangle {
     int x; //position
     int y;
    
     int h;
     int w;
    
     int mvmntx;
     int mvmnty;
    
     color rectColor = color(0,0,0);
      
     Rectangle (int c1x, int c1y) {
       x = c1x;
       y = c1y;
       h = 20;
       w = 20;
       mvmntx = round(random(-2,3)); //movement
       mvmnty = round(random(-2,3));
    
     void boundryCheck() {
       if (x < 0) {
         mvmntx = round(random(1,3));
       }
       if (y < 0) {
         mvmnty = round(random(1,3));
       } 
       if (x+w > windowSize) {
         mvmntx = round(random(-2,0));
       }
       if (y+h > windowSize) {
         mvmnty = round(random(-2,0));
       }
     }
      
     void moveRect() {
       x = x+mvmntx;
       y = y+mvmnty;
     }
    
     void render () {
       fill(rectColor);
       rect(x,y,w,h);
     }
    
     void update() {
       boundryCheck();
       moveRect();
       render();
     }
   }