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Data Structure choices based on requirements

I'm completely new to programming and to java in particular and I am trying to determine which data structure to use for a specific situation. Since I'm not familiar with Data Structures in general, I have no idea what structure does what and what the limitations are with each.
So I have a CSV file with a bunch of items on it, lets say Characters and matching Numbers. So my list looks like this:
A,1,B,2,B,3,C,4,D,5,E,6,E,7,E,8,E,9,F,10......etc.
I need to be able to read this in, and then:
1)display just the letters or just the numbers sorted alphabetically or numerically
2)search to see if an element is contained in either list.
3)search to see if an element pair (for example A - 1 or B-10) is contained in the matching list.
Think of it as an excel spreadsheet with two columns. I need to be able to sort by either column while maintaining the relationship and I need to be able to do an IF column A = some variable AND the corresponding column B contains some other variable, then do such and such.
I need to also be able to insert a pair into the original list at any location. So insert A into list 1 and insert 10 into list 2 but make sure they retain the relationship A-10.
I hope this makes sense and thank you for any help! I am working on purchasing a Data Structures in Java book to work through and trying to sign up for the class at our local college but its only offered every spring...

You could use two sorted Maps such as TreeMap.
One would map Characters to numbers (Map<Character,Number> or something similar). The other would perform the reverse mapping (Map<Number, Character>)
Let's look at your requirements:
1)display just the letters or just the numbers sorted alphabetically
or numerically
Just iterate over one of the maps. The iteration will be ordered.
2)search to see if an element is contained in either list.
Just check the corresponding map. Looking for a number? Check the Map whose keys are numbers.
3)search to see if an element pair (for example A - 1 or B-10) is
contained in the matching list.
Just get() the value for A from the Character map, and check whether that value is 10. If so, then A-10 exists. If there's no value, or the value is not 10, then A-10 doesn't exist.
When adding or removing elements you'd need to take care to modify both maps to keep them in sync.

Why use ArrayList if requirement is not clear?

I have found following question on www.javatpoint.com
If you were to use a List implementation,but not sure which one to, because the requirement is not yet clear. In this case which List implementation will you use ?
options:
1. ArrayList
2. LinkedList
Correct answer for this is ArrayList
But there is no explanation why, Please help me to uderstand

Simple Term
ArrayList : Iterating Over An ArrayList is faster than Linked List, Because All Elements Stored in Contiguous Memory Location. But Performing Operation Like Delete Will Reduce Performance Because Again Entire List Order Changes (Like if you delete element at position 3rd then all next elements location are currentLocation - 1).
LinkedList : Slower When Iteration Performed(As Compare To ArrayList). But Delete and Update Operation Becomes Faster Because If you delete any element at any position only previous and after element locations are changed(Not Entire List).
So When You Don't Have Clear Requirements Just Iteration Is Basic Need (And Array List Gives Best Performance).

One possible reason might be that elements in ArrayList consume less memory space than in LinkedList, because each element in LinkedList contains a value plus a pointer to the next element, while an element in ArrayList has only value

ArrayList stores elements in array in insert order. You can get value by its index in array.
LinkedList stores your elements in Node objects that references each other. Each Node references previous and next Node. You can get elements sequentially starting from both sides. You can also get elements by index but it's not as fast as in ArrayList. Use LinkedList when you need sequential access, like queue or stack data structure

From what I've read in the past: An ArrayList essentially acts as a better array, allowing for dynamic resizing. A LinkedList is a double linked list which causes it to have better performance on adding and removing items from the list, but getting and setting at arbitrary positions is slower than an ArrayList. So, the question is most likely assuming that, generally, a program will be getting and setting values more than it is adding and removing values, which is a fairly reasonable assumption, but the question in question is incorrect.

Number and string sorting Al

I want to sort some number+string combination but the sorting will be based on the number from that combination. Can you suggest an optimal solution?
Say my strings are:
12 Masdf
4 Oasd
44 Twer
and so on. The sorting will be based on the numbers like 12, 4, 44 and after the sorting I have to show the full alphanumeric strings.
As the program will run on thousands of data I don't want to split the string and compare the number on each iteration. My plan is to extract the numbers and take those in an array and then sort the array. After sorting done, I want to put back the numbers with associated strings and keep those in a string array to show.
It should be done in C++. Algorithms should be applied - Insertion sort, Quick sort, Merge sort, etc.

Create a class to store the full string and the number. Make the class Comparable. Convert your list of string to list of Class. Sort the list using which sort method is relevant. Iterate the list and print the string fields.
Sorry, that was an answer for Java, since you tagged it Java. Replace/remove Comparable for whatever is good for C++.

I am going to assume these two parts are in separate variables and are not together as one string (if they were you could just store them in a list).
First consider a Map. Each 'bucket' of the map can be represented by a number. Within each of the maps buckets is a bunch of strings in a list. (Note this could also be solved with an array especially if the Integer part is always under some fixed value) The java equivalent would look like:
Map map = new HashMap<Integer,ArrayList<String>>();
For sorting on this custom collection first the integer part of the value would be searched on the map returning a list. Every item in the list will have the same starting number. So we now search the list the string part of the value (I am assuming the list is sorted so you can do whatever sort you want ie: selection/quicksort).
The advantages of this search mean that if the number is not found in the Hashmap you instantly know there is no string part for it.

Reading an unknown number of items in a web drop down list and storing in an array

I would like code to store an unknown number of integer values from a website's drop-down list into an array and then compare the values in an existing array with the array values retrieved from the drop-down list.
I was thinking maybe a For loop could work? I apologize but I don't have any sample code to put up because I don't know how to start with creating this code. I do have Basic Java knowledge

You can use arraylists, they are dynamic and don't have to be specified size in advance unlike arrays.
List<Integer> integers = new ArrayList<Integer>();
You can add to integers by integers.add();

Adding elements into ArrayList at position larger than the current size

Currently I'm using an ArrayList to store a list of elements, whereby I will need to insert new elements at specific positions. There is a need for me to enter elements at a position larger than the current size. For e.g:
ArrayList<String> arr = new ArrayList<String>();
arr.add(3,"hi");
Now I already know there will be an OutOfBoundsException. Is there another way or another object where I can do this while still keeping the order? This is because I have methods that finds elements based on their index. For e.g.:
ArrayList<String> arr = new ArrayList<String>();
arr.add("hi");
arr.add(0,"hello");
I would expect to find "hi" at index 1 instead of index 0 now.
So in summary, short of manually inserting null into the elements in-between, is there any way to satisfy these two requirements:
Insert elements into position larger than current size
Push existing elements to the right when I insert elements in the middle of the list
I've looked at Java ArrayList add item outside current size, as well as HashMap, but HashMap doesn't satisfy my second criteria. Any help would be greatly appreciated.
P.S. Performance is not really an issue right now.
UPDATE: There have been some questions on why I have these particular requirements, it is because I'm working on operational transformation, where I'm inserting a set of operations into, say, my list (a math formula). Each operation contains a string. As I insert/delete strings into my list, I will dynamically update the unapplied operations (if necessary) through the tracking of each operation that has already been applied. My current solution now is to use a subclass of ArrayList and override some of the methods. I would certainly like to know if there is a more elegant way of doing so though.

Your requirements are contradictory:
... I will need to insert new elements at specific positions.
There is a need for me to enter elements at a position larger than the current size.
These imply that positions are stable; i.e. that an element at a given position remains at that position.
I would expect to find "hi" at index 1 instead of index 0 now.
This states that positions are not stable under some circumstances.
You really need to make up your mind which alternative you need.
If you must have stable positions, use a TreeMap or HashMap. (A TreeMap allows you to iterate the keys in order, but at the cost of more expensive insertion and lookup ... for a large collection.) If necessary, use a "position" key type that allows you to "always" generate a new key that goes between any existing pair of keys.
If you don't have to have stable positions, use an ArrayList, and deal with the case where you have to insert beyond the end position using append.
I fail to see how it is sensible for positions to be stable if you insert beyond the end, and allow instability if you insert in the middle. (Besides, the latter is going to make the former unstable eventually ...)

even you can use TreeMap for maintaining order of keys.

First and foremost, I would say use Map instead of List. I guess your problem can be solved in better way if you use Map. But in any case if you really want to do this with Arraylist
ArrayList<String> a = new ArrayList<String>(); //Create empty list
a.addAll(Arrays.asList( new String[100])); // add n number of strings, actually null . here n is 100, but you will have to decide the ideal value of this, depending upon your requirement.
a.add(7,"hello");
a.add(2,"hi");
a.add(1,"hi2");

Use Vector class to solve this issue.
Vector vector = new Vector();
vector.setSize(100);
vector.set(98, "a");
When "setSize" is set to 100 then all 100 elements gets initialized with null values.

For those who are still dealing with this, you may do it like this.
Object[] array= new Object[10];
array[0]="1";
array[3]= "3";
array[2]="2";
array[7]="7";
List<Object> list= Arrays.asList(array);
But the thing is you need to identify the total size first, this should be just a comment but I do not have much reputation to do that.