function setup() {

  createCanvas(400, 400);

  // ball1=new Ball(width/2,height/2);

  for(let i=0;i<20;i++){

  balls[i]=new Ball(random(width),random(height),random(100))

}

}

function draw() {

  background(0);

 for(let i=0;i<balls.length;i++){

  balls[i].display();

  balls[i].bounce();

}

}

​

class Ball{

  constructor(tempX,tempY,tempD=50,tempXvel=1,tempYvel=2, tempCol=color(255,255,255)){

    this.x=tempX;

    this.y=tempY;

    this.d=tempD;

    this.xVel=tempXvel;

    this.yVel=tempYvel;

    this.col=tempCol;

  }

  display(){

    fill(this.col);

    noStroke();

    circle(this.x,this.y,this.d);

  }

  bounce(){

    this.x+=this.xVel;

    this.y+=this.yVel;

    if(this.x<this.d/2||this.x>width-this.d/2){

      this.xVel*=-1;

    }

     if(this.y<this.d/2||this.y>height-this.d/2){  

      this.yVel*=-1;

    }

  }

}