Trackpad Failing even with Multiple "Repairs"

Question

Hello! I just spend about 25 minutes typing out a detailed email to the apple contact who gave me his contact info personally to follow up with him, but the email failed and said the user did not exist, so I suppose he was either terminated or left the business. Instead of re-hashing everything I am going to literally paste the email I sent him as I don't have much time and i need to finish some class work. Here's the email. (PS. I have tried pretty much everything. and this post is completely sincere and it should fall within apple support guidelines.) This is more of my "story" than anything else.
Hello Mr. Hartly. I know it has been some time since we last spoke, (5 months to be exact), but I wanted to give you an update on my situation. My Macbook Pro SN: C2*****RJ7 was purchased from you several years ago as a refurbished machine and a Christmas present to me from my parents. I cried. It was the best gift I had ever received. Since that day, the laptop has been the car industry's equivalent of a "lemon". Within the first 2 months of having it, the logic board died. This is before I knew anything of computers (I now am very educated in the subject) and I was glad that I could just get it fixed by replacing it. Once this was done, I almost immediately started having issues with my trackpad on the device. When I would use it for any prolonged period of time it seemed the mouse would freeze somewhere on screen and I couldnt move it. Fastforward a year or so after using a magic mouse, and I am starting college. I would like to have a laptop I can actually use in class without toting a separate mouse that defeats the purpose and convenience of having a laptop, so I take it in again to be worked on. They tell me at Computers Plus in Corridor G in West Virginia ********, the nearest "certified apple repair store" that it is almost definitely a bad trackpad. I fork over more cash to get it replaced. The issue happens within 20 minutes of getting home. I call them back and they say to bring it back in and they would fix it for free, after a week of having my laptop they replace my hard drive and charge me 50 dollars for it and said they "didnt charge me for the labor." like i should be thankful. Fed up at this point, I contact your support team via phone. They were very helpful and I ended up speaking to you ( you can look up my old repair ID: ********.) after speaking to you, you told me to send it to you and you would fix it free of charge. I was so excited at this point. ECSTATIC even. I'm finally going to have an apple macbook pro! I love editing videos and I couldnt wait to install my software onto the laptop and get to work. The fixing process happened extremely quickly. I had it back in less than 2 days which made me nervous considering the fact that the local shop had it for a week. I read what the note in the box said. "1 Replaced Trackpad". So thats 2 trackpads now. I test it out and it still freezes after a couple hours of use. After emailing you, you suggest that I completely reinstall OS X onto the device. Frustrated and put out by the run around and lack of fixes, I put it aside for a while as classes started. About a month and a half ago, I was bored and wanted to do some tinkering, so I made an OS X usb bootable and reinstalled the OS. So excited to see if it worked, I started going through the initial setup and initial menus. about an hour after installing the os and doing some classwork/watching some media, guess what. Freeze. Unresponsive. Frustration. Defeat. I sit the machine aside and tried to forget about everything. No one was going to help me, and I have already spent so much money, that I could have just gotten a NEW MAC TO BEGIN WITH. I could honestly cry when I think about it. Fast-forward a month or so to last week.
Just the other day, I pull out the machine to let my girlfriend do some classwork on, and she complains that the trackpad is unresponsive and asks for a mouse. Frustrated, I give it to her the magic mouse. With the frustrations and disappointment fresh in my mind, I make a note to find your email address and tell you my whole story from beginning to end. I don't want other people to have the same experience as me. I truly do not want this to be taken as a disgruntled and frustrated boy; I haven't spoken negatively to anyone about the incident and I haven't raged about or talked about it on social media. I WANT apple to succeed. I think you're one of the greatest, if not THE greatest producer of technology on the planet. But right now I'm just a young man taking college classes from his bedroom in need of a working laptop. Thanks for your time and for reading this,
With all my respect,
Lukas
<Personal Information Edited by Host>

Answer 1

An Iterator.delete() has the spec:
public void remove()
Removes from the underlying collection the last element returned by the iterator (optional operation). This method can be called only once per call to next. The behavior of an iterator is unspecified if the underlying collection is modified while the iteration is in progress in any way other than by calling this method.
So when in your example the second iterator modifies the underlying collection it breaks the first instance iterator behavior which has then an unpredictable result.
Using a List.iterator() seems to change nothing :
public Iterator iterator()
Returns an iterator over the elements in this list in proper sequence.
Specified by:
iterator in interface Collection
Returns:
an iterator over the elements in this list in proper sequence.
So you code isn't garanty to run as you quote it running. The i2 is safe not i1 if you use i2.remove().
I did this test:
     List v1 = new Vector();
     v1.add("1");
     v1.add("2");
     v1.add("3");
     Iterator i1 = v1.iterator();
     while (i1.hasNext()) {
          Object o1 = i1.next(); // At second iteration I got a ConcurrentModificationException here.
          Iterator i2 = v1.iterator();
          while (i2.hasNext()) {
               i2.next();
               i2.remove();
          System.out.println(o1);
That's a typical unexpected results because hasNext() answered true but next() failed.
Now if your question is why this spec, I dunno, I could only guess that the purpose of Iterator generic interface is to allow to have efficient implementation at price of non concurent modification access.