I'm curious about some things; for example, user is never defined, and index is hardly fifty in length... I suppose that this is merely a representation of the problem. Regardless: I think it will work better if you remove the else statement.

You are right, I forgot to include them in this example (edited now). I have also tried removing the else statement.

I think i found something: Even after finding a match the continues evaluating though changing checkThe Name before returning. I added a return inside the if test (line 27) and it seems to work, try:

As said above:

1. void setup()
2. {
3.   MessageClass test2 = new MessageClass("Two");
4.   println(test2.indexNumber());
5.   MessageClass testx = new MessageClass("Xool");
6.   println(testx.indexNumber());
7.   exit();
8. }
9.  
10. class MessageClass {
11.   String[] index = {
12.     "One", "Two", "Three"
13.   };
14.   String user;
15.  
16.   MessageClass (String user) {
17.     this.user = user;
18.   }
19.  
20.   int indexNumber() {
21.     for (int i = 0; i < index.length; i++) {
22.       if (user.equals(index[i])) {
23.         return i;
24.       }
25.     }
26.     return -1;
27.   }
28. }

Don't forget indexes start at 0.
Perhaps you might prefer:

1.   int indexNumber() {
2.     for (int i = 0; i < index.length; i++) {
3.       if (user.equals(index[i])) {
4.         return i+1;
5.       }
6.     }
7.     return 0;
8.   }

Hi,

I wonder why you want to add a array when you create a class. Because for every entity of this class there is allot of memory consumed.
I made a different version :

1. MessageClass test;
2. HashMap hm = new HashMap();
3. void setup() { 
4.   hm.put("Zero", 0);
5.   hm.put("One", 1);
6.   hm.put("Two", 2);
7.   hm.put("Three", 3);
8.   test = new MessageClass("Two");
9.   println(test.indexNumber());
10.   test = new MessageClass("Zero");
11.   println(test.indexNumber());
12.   test = new MessageClass("Three");
13.   println(test.indexNumber());
14.   test = new MessageClass("Four");
15.   println(test.indexNumber());
16. }
17. class MessageClass {
18.   String user;
19.   MessageClass (String user) {
20.     this.user = user;
21.   }
22.   String indexNumber() {
23.     try {
24.       Object value = hm.get(user);
25.       return value.toString();
26.     }
27.     catch (NullPointerException e) {
28.       return ""+false;
29.     }
30.   }
31. }

"Because for every entity of this class there is allot of memory consumed."
It is a minor problem here, and if your solution is better for large data, it is a bit of overkill for a new user.

Note: one can make the class static, and the array too, to share the data across classes.

Many thanks for the responses. I have tried them all, nothing works except explicitly stating the items of the array:

"nothing works"
Define "works". What do you expect, what do you get.
I tested my code, so I know my code works, with regard with what I expected...

Nothing works inside the rest of my code, which asks to check 50 items inside the array. 

Don't you wanna post it? 

Actually, I wonder what you are trying to do. Why do you compute an index each time, instead of storing it in the class, for example. What is the purpose of this code.
It is a good thing you isolated your problem in a simple sketch, but apparently it was too isolated...

I've tried to clean the code a little bit. I hope this gives you a more clear idea of what I am trying to do:

Change:

1.   for (int i = 0; i < data.length; i++) {
2.     MessagesArray.add(new MessageClass (data[i], randomizeX, randomizeY));
3.   }
4.   for (int i = 0; i < MessagesArray.size(); i++) {
5.     images = new PImage[i];
6.     images[i] = loadImage(i + ".jpg");
7.   }

(it cannot work, you reinitialize the images array on each loop!)
to:

1.   for (int i = 0; i < data.length; i++) {
2.     PImage image = loadImage(i + ".jpg");
3.     MessagesArray.add(new MessageClass(data[i], image, randomizeX, randomizeY));
4.   }

and of course, add a PImage field to your MessageClass and to its constructor.
Thus, you can get the image from the messageInstance1 instead of picking it from a separate array by computing some index in a convoluted way.
Alternatively, you can also store i in the MessageClass to determine its index / id, or just use the i index in the loop in draw(), etc.
Storing the image in the class is probably the best way (unless, perhaps, two instances of the class can use the same image, but even then they can share the image).

I remain sketchy on purpose (and because of lack of time), but if you need more details, just ask.

It makes sense now.