Integer into Linked List in an array

Disclaimer: I ranted a bit. I'm just trying to put everything down that is relevant. If you're only interested in the solution scroll down to where I have bolded a heading...

Starting from the beginning, like Nathaniel Ford mentioned I believe you have a conceptual misunderstanding of how a HashTable implementation works. Let's start by breaking down the logic.

A HashTable is a construct used to store and quickly retrieve objects by computing a unique (or nearly unique) hash of the object you're storing. When you compute this one way hash and use it to store an object in the table you allow O(1) lookup at ideal cases.

In a perfect world all inputs would hash uniquely and there would never be a collision but we know that is not practical. So when you have more than one object you need to have a collection that allows you to store multiple objects to the same hash value; a LinkedList!

Now with a set array of 12 values you need to have a unique LinkedList for each element. Your expected output if written out would be like this:

hashTable[0] = LinkedList(Node(36) -> Node(60) -> Node(108) -> Node(312))
hashTable[1] = LinkedList(Node(85))
etc...

Currently you're attempting to mash the idea of a single linked list together with the collection of linked lists. We see this misunderstanding here:

private static MyList last;
private static MyList first;

By declaring first and last as class variables you're essentially creating the belief that there is ever only one first and one last variable for the entire collection of Linked Lists where each list individually should have its own first/last pointers. What the result of your code creates is logic where Nodes inserted to various positions in the array have references to positions that are entirely unrelated to them.

So in reality, where to start fixing?

Clean up your insert method in such you take things step by step.

1) Compute the incoming object's hash
2) Lookup the hash on the array
3) If the array location is null, generate a new Linked List and insert the value into the array
3b) If the array is not null, create a new node for the list and point the final node of the existing list to the new node
4) Done

Nathaniel's code is perfect for this need but if you're forced to use the MyList implementation it would behave something like this:

int hash = searchKey % arr.length;
MyList newNode = new MyList(searchKey);
MyList arrIndex = arr[hash];

if (arrIndex == null) {
  arr[hash] = newNode;
} else {
  while (arrIndex.next != null) { 
    arrIndex = arrIndex.next;
  }
  arrIndex.next = newNode;
}

Additionally your printHash method has need of updating due to two issues.

1) Your logic for increasing i in the event arr[i] is null can cause you to go out of bounds. In the case where the last index of the array is null you would increase i without ever checking it. You're better off doing a check like this and letting the loop do the work for you:

if (anArray[i] == null) {
  continue;
}

or to keep code more clean (no random jumps in program flow)

for (...) {
  if (anArray[i] != null) {
    //Code to print that array
  }
}

2) Without using first and last anymore you just iterate over each element

for (int i = 0; i < anArray.length; i++) {
  System.out.print("\nThe items for index[" + i + "]: ");

  if (anArray[i] != null) {
    MyList tmp = anArray[i];
    while ((tmp = tmp.next) != null) {
      System.out.print(tmp.iData + " ");
    }
  }
}