Hi there,
I am sure this is a stupid noob question, but I just can't seem to understand how to pass data between objects.  In this particular example, I want to calculate the distance between two different objects.

Basically, I want to create a shape (obj 1) that responds to the distance from a point (obj 2).  Later, there will be multiple shapes and points.

I have this working inside a draw, but when I try to convert it into objects I run into all sorts of problems.  I have included the code below.  The commented out part is the non-working part.

Code:

Component a;
VectorPoint p;

void setup() {
  size (600, 300);
  a = new Component(100., 100.);
  p = new VectorPoint (200., 200.);
  
}

void draw() {
  background (160);
//  a.display();
  p.display();
  
}

void mouseDragged() {
  p.update();
}


class Component {

  // Methods
  VectorPoint scalePoint;
  PVector center;

  PVector p1, p2, p3, p4;
  PVector v1, v2, v3, v4;

  float componentMin = 20.;
  float componentMax = 60.;

  // Constructor
  Component (float cx_, float cy_) {

    scalePoint = new VectorPoint(400,100);
    center = new PVector (cx_, cy_);

    p1 = new PVector (center.x + 30, center.y - 30);
    p2 = new PVector (center.x - 30, center.y - 30);
    p3 = new PVector (center.x - 30, center.y + 30);
    p4 = new PVector (center.x + 30, center.y + 30);

    v1 = new PVector (0,0);
    v2 = new PVector (0,0);
    v3 = new PVector (0,0);
    v4 = new PVector (0,0);
  }

  void display() {
    // Calculate the maximum size possible on the screen
    float maxSize = sqrt (width*width + height*height);

    // Inner square to calculate the distances
    ellipse (p1.x, p1.y, 5, 5);
    ellipse (p2.x, p2.y, 5, 5);
    ellipse (p3.x, p3.y, 5, 5);
    ellipse (p4.x, p4.y, 5, 5);
/*
    // Distances from scalePoint to point on inner square
    float m1 = PVector.dist (scalePoint, p1);
    float m2 = PVector.dist (scalePoint, p2);
    float m3 = PVector.dist (scalePoint, p3);
    float m4 = PVector.dist (scalePoint, p4);

    float magnitude1 = map(m1, 0, maxSize, componentMin, componentMax);
    float magnitude2 = map(m2, 0, maxSize, componentMin, componentMax);
    float magnitude3 = map(m3, 0, maxSize, componentMin, componentMax);
    float magnitude4 = map(m4, 0, maxSize, componentMin, componentMax);

    v1.set ((center.x + (magnitude1 * cos ((7*PI) / 4))), (center.y + (magnitude1 * sin ((7*PI) / 4))), 0);
    v2.set ((center.x + (magnitude2 * cos ((5*PI) / 4))), (center.y + (magnitude2 * sin ((5*PI) / 4))), 0);
    v3.set ((center.x + (magnitude3 * cos ((3*PI) / 4))), (center.y + (magnitude3 * sin ((3*PI) / 4))), 0);
    v4.set ((center.x + (magnitude4 * cos ((PI) / 4))), (center.y + (magnitude4 * sin ((PI) / 4))), 0);

    // The component - center lines
    strokeWeight(0.5);
    ellipse (center.x, center.y, 10, 10);
    line (center.x, center.y, v1.x, v1.y);
    line (center.x, center.y, v2.x, v2.y);
    line (center.x, center.y, v3.x, v3.y);
    line (center.x, center.y, v4.x, v4.y);

    // The component - border edges
    strokeWeight(1);
    line (v1.x, v1.y, v2.x, v2.y);
    line (v2.x, v2.y, v3.x, v3.y);
    line (v3.x, v3.y, v4.x, v4.y);
    line (v4.x, v4.y, v1.x, v1.y);

    // Line from center to scalePoint
    //line (center.x, center.y, scalePoint.x, scalePoint.y);
    */
  }   
}


class VectorPoint {
  PVector vp;

  VectorPoint (float x_, float y_) {
    vp = new PVector (x_, y_);
  }

  void display() {

    // Scale Point
    strokeWeight(0.5);
    ellipse (vp.x, vp.y, 10, 10);
    line (vp.x - 10, vp.y, vp.x + 10, vp.y);
    line (vp.x, vp.y - 10, vp.x, vp.y + 10);


  }

  void update() {
    if (dist(mouseX, mouseY, vp.x, vp.y) < 10) {
      vp.x += (mouseX - pmouseX);
      vp.y += (mouseY - pmouseY);
    }
  }
}
 

I haven't looked at all the code but I think I can answer your base question.
To have two objects to interact (eg. one computing the distance to another), you just have to pass the second object to the first one. It might be as a one shot parameter to a function, or it might become a field of the object, either by giving it in the constructor or by setting it later in a setter function (just assigning the parameter to the field).
Of course, you can also just pass some fields of the second object in methods call on the first one:

A a = new A();
B b = new B(); // or B b = new B(a);
b.setA(a); // => B has a A myA field and does myA = a
// or
b.doStuff(a);
// or
b.doOtherStuff(a.f); // or a.getF()

I think it is possible... But I don't understand the problem. Where are you stuck?

I am stuck with this part:
Code:

float m1 = PVector.dist (scalePoint, p1); 

I want to be able to pass the coordinates of the scalePoint into the PVector.dist . I am sure there is a simple answer, but I can't seem to find it.

As to why, I wanted to write it as a class because the plan is to use many of them in an ArrayList.

Aha!

Thanks antiplastik - now I understand!