http://processing.org/learning/objects/
Very nice explanation on classes for coding in Processing (Java).
Why you need classes: Imagine coding 100 ants XD
Simply change the attributes in the constructor and there we go :P

Slowly work your way through this pile of information ;)
http://processing.org/learning/

here is the code as it is in the assignment that you have to fill out....

now you can the properties of the bug after line 45:

• pos as x and y.
• color bugColor = color (random(255),random(255),random(255));
• the walk direction of it
• etc.

 

1. // BugHunt
2. // CMPS 5J
3. // pa7
4.  
5. int n = 100;           // number of bugs
6. Bug[] B = new Bug[n];  // bug array
7. int clickCount = 0;
8. int deadCount = 0;
9. float killRate;
10.  
11. void setup(){
12.   size(500,500);
13.   smooth();
14.   for(int i=0; i<n; i++){
15.     B[i] = new Bug(random(20,480),random(20,480),(int)random(1,5));
16.   }
17. }
18.  
19. void draw(){
20.   background(170);
21.   for(int i=0; i<n; i++){
22.     B[i].display();
23.     B[i].crawl();
24.   }
25. }
26.  
27. void mousePressed(){
28.   clickCount++;
29.   for(int i=0; i<n; i++){
30.     if( B[i].mouseOn() ){
31.       B[i].squash();
32.       deadCount++;
33.     }else if( B[i].scared() ){
34.       B[i].runAway();
35.     }
36.   }
37.   killRate = float(deadCount)/clickCount;
38.   println("kill rate = "+killRate);
39. }
40.  
41.  
42. // =========================================
43.  
44. class Bug{
45.   // fields
46.  
47.   // constructor
48.   Bug(float x, float y, int s){
49.  
50.   }
51.  
52.   // methods
53.   void crawl(){
54.  
55.   }
56.  
57.   void display(){
58.  
59.   }
60.  
61.   void squash(){
62.  
63.   }
64.  
65.   void runAway(){
66.  
67.   }
68.  
69.   boolean mouseOn(){
70.  
71.   }
72.  
73.   boolean scared(){
74.  
75.   }
76. }

Hello!

You can see an algorithm example for mouse-over in this Poppable Balloons game:

http://studio.processingtogether.com/sp/pad/export/ro.9V7R1wu55fOiN/latest

Look for method isHit() inside class Balloon!