Vectors/Arrays Mixed with Classes

Question

Here's my problem
I'm have a for loop which collects integers, (i). What'd I'd like to do is make a list of all the numbers "i" comes up as, and then record how many times "i" comes up as a certain number.
For example,
say the for loop is retrieving the number 1,5,7,3,1,1,6,3,4,5,7
I'd like to create some type of data structure that will do this:
Numbers/Instances
1/3
3/2
4/1
5/2
6/1
7/2
I do NOT need it to say that there are no instances of 2, for example, but if it did I could live with that.
I thought of creating a Class containing a variable for instances, and then making an array, where the index value would be the number and the variable would be the instances... so... say:
The class name is Numbers, with public static int times:
Numbers [] myNum=new Numbers[10];
The problem with an array is that you can't resize it. I also have no guarantee that the numbers will stay below any certain number. While I could simply define myNum as having a million slots to be sure, I don't think its the best way.
On the other hand, I can't figure out how to create a vector from a class, as you can't simply:
Vector Numbers myBum=new Vector();
I figured vectors would work well as their size is extremely flexible, however if I can't somehow get it to keep track of instances, I'm not working well.
I was thinking of using hash tables, but I don't completely understand them... while I could somehow tell it to treat each collision as an instance, and add them, wouldn't some hash keys be shared among different numbers (ie perhaps 7 and 43 share the same hash key?) Like I said, I don't completely understand them, so I'm not sure if I'm doing something wrong. I used a hash table to sort strings once and it threw a lot of completely different words in the same part of the has table.
Any help you can offer would be extremely appreciated. This is a huge mental block thing more than anything, I think. I'm sure there's a practical way to do this in Java.
Regards,
Alessandro

Answer 1

Whenever an Object in Java is created, its original type is remembered. Thus,
Object a = new Vector();
Vector my_vector = (Vector)(a);is a valid cast, since "a" was a Vector to start with. Therefore, supposing you have a mutable number-counting object NumberCount, you could simply do the following:
NumberCount count = new NumberCount(my_number);
Vector count_vector = new Vector();
count_vector.add(count);
NumberCount inc_count = (NumberCount)(count_vector.get(index));
inc_count.increment();For this project, I would personally recommend a Hashtable. A Hashtable is a type of Map; a Map contains a set of keys, each of which is mapped to a value. Keys are guaranteed to be unique. The only problem, however, is that putting a value into a Hashtable with a key that already exists in the Hashtable destroys the Hashtable's record of the old value.
Thus, you could have...
Hashtable table = new Hashtable();
table.put(new Integer(1),count_value);
table.get(new Integer(1),count_value.increment());Be careful with this approach; creating new Integer objects like this can be very costly on the garbage collector and will slow your program down if you do it too intensively. But that's another issue. ;)