arc() will draw part of a circle between two points

http://processing.org/reference/arc_.html

bezier() and curve() will draw more complex shapes:

http://processing.org/reference/bezier_.html
http://processing.org/reference/curve_.html

now, what if I got tons of random circles and i want to connect them all together (like a network system or something like that) by using arcs or circles, how to do that? I don't know how to get the position of a random circle and connect it to another one.

I think I understand you...
Just store the random number in a variable and use it more than once...

Could you show me a short example how to do that please? I'm a total beginner to processing.

Thank you I tried it out already! but the problem is the line is all connected into a point (200,200). I would like to connect all the circles together. 

Here's a sweet example for you:

1. class Circle{
2.   float x, y, r;
3.   color c;
4.   Circle(){
5.     x = random(width);
6.     y = random(height);
7.     r = random(10,20);
8.     c = color( random(255), random(255), random(255) );
9.   }
10.   void draw(){
11.     pushStyle();
12.     ellipseMode( CENTER );
13.     fill(c);
14.     stroke(0);
15.     ellipse( x, y, r, r );
16.     popStyle(); 
17.   }
18. }
19. Circle[] circles;
20. void setup(){
21.   size(400,400);
22.   smooth();
23.   circles = new Circle[20];
24.   for( int i = 0; i < circles.length; i++ ){
25.     circles[i] = new Circle();
26.   }
27. //}
28. //void draw(){
29.   background(128);
30.   stroke(0);
31.   noFill();
32.   for( int i = 0; i < circles.length-1; i++ ){
33.     bezier( circles[i].x, circles[i].y, circles[i+1].x, circles[i].y, circles[i].x, circles[i+1].y, circles[i+1].x, circles[i+1].y );
34.   }
35.   for( int i = 0; i < circles.length; i++ ){
36.     circles[i].draw();
37.   }
38. }

too late...   

1. // from http://processing.org/learning/topics/arraylistclass.html
2. ArrayList <Ball> balls;
3. final int numBalls=4;
4. final int ballWidth = 48;
5. final String helpText = "Mouse - new circle; key - new picture";
6. // =====================================================================
7. void setup() {
8.   size(500, 500);
9.   smooth();
10.   // Create an empty ArrayList
11.   balls = new ArrayList();
12.   // initCircles
13.   newList();
14. }
15. void draw() {
16.   // delete
17.   background(111);
18.   // show balls
19.   // With an array, we say balls.length, with an ArrayList, we say balls.size()
20.   // The length of an ArrayList is dynamic
21.   for (Ball ball : balls) {
22.     ball.display();
23.   }
24.   // help text
25.   fill(244);
26.   text(helpText, 10, 17);
27. }
28. void newList() {
29.   balls.clear();
30.   // Start by adding elements
31.   for (int i=0; i<numBalls; i++) {
32.     balls.add(new Ball(
33.     random(30, width-30), random(30, height-30),
34.     ballWidth,
35.     color (random(0, 255), random(0, 255), random(0, 255))));
36.   }
37. }
38. // =====================================================================
39. void mousePressed() {
40.   // A new ball object is added to the ArrayList (by default to the end)
41.   balls.add(new Ball(mouseX, mouseY, ballWidth,
42.   color (random(0, 255), random(0, 255), random(0, 255))));
43. }
44. void keyPressed() {
45.   // new picture
46.   newList() ;
47. }
48. // =====================================================================
49. // Simple ball class
50. class Ball {
51.   float x;
52.   float y;
53.   color myColor;
54.   float w;
55.   int connectTo=-1;
56.   Ball(float tempX, float tempY,
57.   float tempW,
58.   color tempmyColor1) {
59.     x = tempX;
60.     y = tempY;
61.     w = tempW;
62.     myColor=tempmyColor1;
63.     connectTo=(int)random(balls.size()-1);
64.   }
65.   void display() {
66.     // Display the circle
67.     noFill();
68.     stroke(myColor);    
69.     ellipse(x, y, w, w);
70.     //
71.     if (connectTo!=-1) {
72.       Ball connectToCircle = balls.get(connectTo);
73.       if (x!=connectToCircle.x) {
74.         /*
75.         // red
76.          stroke(222, 4, 6);
77.          bezier(x, y,
78.          x+connectToCircle.x, y+connectToCircle.y,
79.          connectToCircle.x*.8, connectToCircle.y*.8,
80.          connectToCircle.x, connectToCircle.y
81.          );
82.          */
83.         //blue
84.         stroke(2, 2, 222);
85.         float addValue=dist(x, y,
86.         connectToCircle.x, connectToCircle.y);
87.         addValue*=.4;
88.         bezier(x, y,
89.         (x+addValue), (y+addValue),
90.         connectToCircle.x+addValue, connectToCircle.y+addValue,
91.         connectToCircle.x, connectToCircle.y
92.           );
93.       } // if
94.     } // if
95.   } // method
96.   //
97. } // class
98. // =====================================================================

@_@ i think it's a little bit too much for me... but anyway, thanks a lot for helping me. Just one more thing, I'm using Python language but based on processing.py. It would be the best if you help translate these codes into python. def, class and things... different @_@ sorry, but i'm confused much about coding

I don't know Python language but it would be nice if you would tell that before people write code for you in the wrong language,,,,

I know, sorry about that...