Processing already adds quite a fe of those to your code when you hit go.

That is pure java code, processing is a layer on top of java, so pure java examples you find on the web aren't going to "just work" inside processing.

If you want to use that code, don't use processing, use something like eclipse which is just a normal Java compiler/editor.

If you want to use procesing, look for specific processing examples to learn from, not normal java ones.

//by Alessandro Capozzo - GHOSTAGENCY.NET
// 6 November 2003

Ball [] cont;
float n=0.00f;
float q=0.03f;
int num=5;
float dens;
float nnn;
int nn;

void setup() {
 size(200,200,P3D);
 frameRate(60);
 cont=new Ball[num];
 for (int index = 0; index < num; index++) {
   cont[index]=new Ball(10/((25.5f)*(index+1)),100,100,15);
loadPixels();
 }

}

void draw() {
 background(250);
 n=n+0.1f;
 for (int index = 0; index < num; index++){
   cont[index].update();
 }

 for (int _x = 0; _x < width; _x++) {
   for (int _y = 0; _y < height; _y++) {
     dens = 0;
     for (int res = 0; res <num; res++) {
       dens +=cont[res].dim/(sqrt(sq(_x - cont[res].bx) + sq(_y - cont[res].by)));
     }
     nn=(int)((dens)*(150));
     nnn=50*( noise(_x*q,_y*q,n));

     int c=color(nn-nnn,(nn-nnn)*0.8f,(nn-nnn)*0.5f);
     pixels[_y*width+_x] =c;

   }
 }
updatePixels();
}

class Ball {
 int bx,by;
 int difX,difY;
 int dim;
 float xSpeed,ySpeed,ndelay;

 Ball(float d,int initX,int initY,int magnitude){
   ndelay=d;
   bx=initX;
   by=initY;
   difX=0;
   difY=0;
   xSpeed=0.00f;
   ySpeed=0.00f;
   dim=magnitude;

 }
 void update (){
   difX=mouseX-bx;
   difY=mouseY-by;
   xSpeed+=difX*ndelay;
   ySpeed+=difY*ndelay;
   xSpeed*=.9f;
   ySpeed*=.9f;
   bx+=xSpeed;
   by+=ySpeed;

 }
}