I want to create letters stick together by pisica. but I dont know how to add it to my code~~ how to change balls to letters~~
Just like this:

import fisica.*;

FWorld world;

color bodyColor = #6E0595;


int spiderCount = 10;
int mainSize = 40;

ArrayList balls = new ArrayList();

void setup() {
  size(400, 400);
  smooth();

  Fisica.init(this);

  world = new FWorld();
  world.setGravity(0, 0);

  for (int i=0; i<spiderCount; i++) {
    createSpider();
  }
}

void draw() {
  background(255);

  world.step();
  world.draw();
}

void createSpider() {
  float posX = random(mainSize/2, width-mainSize/2);
  float posY = random(mainSize/2, height-mainSize/2);
  FCircle balls = new FCircle(mainSize);
  balls.setPosition(posX, posY);
  balls.setVelocity(random(-20,20), random(-20,20));
  balls.setFillColor(bodyColor);
  balls.setNoStroke();
  balls.setGroupIndex(2);
  world.add(balls);
 
}

Here is my code:
import rita.*;
import ddf.minim.*;
import fisica.*;

ArrayList balls;
String[] a = {
  "a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y", "z"
};

int global_counter = 0;
int global_counter_limit = 40;

//float easing = 0.005;

int pause_counter_limit = 200;

float START_FRAMES = 150;

boolean clicked = false;

//RiText rt;

FWorld world;

PFont font;

Minim minim;


  Fisica.init(this);

  world = new FWorld();
  world.setGravity(0, 0);
}



void draw() {

  background(255);
  int i = floor(random(0, a.length));//string


  global_counter++;
  float r = 15;

  if (global_counter >= global_counter_limit) { 
    balls.add(new Ball(random(width), r, a[i]));
    global_counter = 0;
  }


  for (int j=0; j< balls.size(); j++) {//arraylist
    Ball ball = (Ball)balls.get(j);

    ball.Ball_jump(4);
    ball.Ball_display();
    ball.Ball_move();
    ball.Ball_bounce();
    ball.Ball_interact();
  }

  //world.step();
  //world.draw();

  drawGameStart();
}

void drawGameStart() {

  float progress = (START_FRAMES - frameCount) / START_FRAMES;

  float opacity = max(0, 255 * progress);

  fill(0, 0, 0, opacity/1);
  noStroke();
  rect(0, 0, width * 2, height * 2);


  font = loadFont("Papyrus-Condensed-40.vlw");
  textFont(font);
  textSize(70);
  int count = floor(progress * 3) + 1;
  if (count < 1) {
    fill(255, 255, 255, 0);
    text(count, 520, 170);
  }
  else
  {
    fill(255, 255, 255);
    text(count, 520, 170);
  }

  //interact();
}


Class Ball:

class Ball {

  float x = width/2;
  float y = random(10, 60);
  float y_old;
  float r = 15;
  float v = 0;
  String str = "0";

  //int c;

  float acc = 0;
  float da = .6;
  float viscosity = .3;

  float pause_counter;

  int dx = 0;
  int dy = 0;

  Ball(float x, float r, String str) {
    this.x = x;
    this.r = r;
    this.str = str;

    pause_counter = 0;
  }

  void Ball_jump(int magnitude) {

    dx = (int)random(-magnitude/2, magnitude/2);
    dy = (int)random(-magnitude/2, magnitude/2);
  }

  void Ball_display() {
    fill(0);

    pushMatrix();


    translate(x, y);
   
    if(y < 60) {
    translate(dx, dy);
    }

    font = loadFont("YuppyTC-Regular-40.vlw");
    textFont(font);
    textSize(r);
    text(str, 0, 0);

    popMatrix();
  }



  void Ball_move() {
    /*
    // attract to opposite charges
     int n = balls.size();
    
     for (int i=0; i<n; i++) {
     Ball b = (Ball)balls.get(i);
     if (b==this) continue;
     float d = dist(x, y, b.x, b.y);
     float dd = min(500 / d, 1);
     float f = (c != b.c) ? dd : -dd;
     float dir = atan2(b.y-y, b.x-x);
     x += f * cos(dir) * easing;
     y += f * sin(dir) * easing;
     }
     */

    float posX = random(r/2, width-r/2);
    float posY = random(r/2, height-r/2);
    FCircle balls = new FCircle(r);
    balls.setPosition(posX, posY);
    balls.setVelocity(random(-20, 20), random(-20, 20));
    balls.setNoStroke();
    balls.setGroupIndex(2);
    world.add(balls);


    pause_counter++;
  }

  void Ball_bounce() {

    y_old = y;

    if (pause_counter > pause_counter_limit) {

      acc = acc + da;
      v = v + acc;
      v = v * viscosity;
      y = y + v;
    }

    if (y+r/2 > height) {
      if (y_old+r/2 >height) {
        y = height - r/2;
      }
    }

    if (y + r/2 > height) {
      v = v * -.45;
      acc = acc * -.45;
    }
  }
  void Ball_interact() {

    if ((clicked == true) && (y == height - r/2)) {
      text(str, mouseX, mouseY, r, r);
    }
    //ball.Ball_display();
    //ball.Ball_move();
    //ball.Ball_bounce();
  }

  void mousePressed() {
    if (clicked == true)
    {
      clicked = false;
    }
    else {
      clicked = true;
    }
  }
}

Thank you!!