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How do I store the values in best java collection structure

What type of collection structure would be best suited for below structure .
I want to create a rows of start and end positions and wanted to store it as a structure. based on the number of occurrences I want to execute a function .
Example
StartPosition Endposition
1 5
6 9
10 14
15 18
Now I want to store the the values like ( (1,5) , (6,9) , (10,14) , (15,18) )
Now I want to execute a function 4 times as I have 4 occurrences
for (i=1 , i <4 , i ++)
{
f(xyz , Startposition , endposition)
}

I suggest you use create a simple class and a List<> of this class.
public class Range{
private int start;
private int end;
// constructor
// gets and setts
}
And you would use like this:
List<Range> ranges = new ArrayList<>();
ranges.add(new Range(1,5));
ranges.add(new Range(6,9));
...
ranges.add(new Range(x,y));
for(Range range : ranges){
f(xyz, range.getStart(), range.getEnd());
}

As I understand, two dimensional array would do. Do you have any reason why you want a collection here?

Option 1: use Array. This is very simple.
int[] arr = { 1, 5, 6, 9, 10, 14, 15, 18 };
for (int i = 0; i < arr.length; i += 2) {
int start = arr[i];
int end = arr[i + 1];
// payload
}
Option 2: use TreeSet with custom comparator. A little bit more difficult, but code is more clear.
Set<Pair<Integer, Integer>> ranges = new TreeSet<>(Comparator.comparingInt((ToIntFunction<Pair<Integer, Integer>>)Pair::getKey).thenComparingInt(Pair::getValue));
ranges.add(new Pair<>(1, 5));
ranges.add(new Pair<>(6, 9));
ranges.add(new Pair<>(10, 14));
ranges.add(new Pair<>(15, 18));
for (Pair<Integer, Integer> range : ranges) {
int start = range.getKey();
int end = range.getValue();
// payload
}

You can use built in java.awt.Point class to set X,Y values. Stores those objects in either java.util.ArrayList or java.util.LinkedList

How to change an element in a list of lists Java

This is a peice of my code, i am making a grid of 5x5 with random colors set to each section. I need to set the specified y_loc and x_loc in the list to the color randomly picked except i have not been able to find out how. It should be the second last line that is not operating as id like. I understand that i could do this in much much longer code but it would be nice to do it in less.
//making the map
ArrayList<ArrayList<String>> fullmap = new ArrayList<ArrayList<String>>();
ArrayList<String> y_row_0 = new ArrayList<String>();
ArrayList<String> y_row_1 = new ArrayList<String>();
ArrayList<String> y_row_2 = new ArrayList<String>();
ArrayList<String> y_row_3 = new ArrayList<String>();
ArrayList<String> y_row_4 = new ArrayList<String>();
//adding each row
fullmap.add(y_row_0);
fullmap.add(y_row_1);
fullmap.add(y_row_2);
fullmap.add(y_row_3);
fullmap.add(y_row_4);
Random rn = new Random();
//loop to randomly pick colors then set them to their destined locations
for (int y_loc = 0; y_loc < 6; y_loc++){
for (int x_loc = 0; x_loc < 6; x_loc++){
colorPicked = false;
while (!colorPicked){
int ranNum = rn.nextInt();
if (ranNum ==0){
if (redTot < 5) {
redTot += 1;
fullmap.set(y_loc).set(x_loc, "Red"));
colorPicked = true;

Since you have lists in list here, to set something at a specific location, you'll have to get the inner list and then perform the set on it.
The following should work:
fullmap.get(y_loc).set(x_loc, "Red"));
Also, since you seem to always have a 5x5 matrix, I'd recommend using a double array instead. That'd make that line:
fullmap[x_loc][y_loc] = "Red";

You should have something like this:
fullmap.get(y_loc).set(x_loc, "Red"));
Notice the "get". You are "getting" the list at the y location, which returns an array list, then calling "set" against that array list to set the actual value in the index of the "x_loc" value.

You need to make a couple of changes:
While declaring the sub lists, you need to make sure they have 5 empty/null elements. Otherwise set will throw IndexOutOfBoundsException. E.g. you need to declare the lists like this:
ArrayList<String> y_row_0 = Arrays.asList(new String[5]);//Assuming it will have 5 elements
While setting the element, you first need to get the corresponding sub list, e.g. the following needs to be changed from:
fullmap.set(y_loc).set(x_loc, "Red"));
to
fullmap.get(y_loc).set(x_loc, "Red"));

Others have already discussed the indexing issue. Apart from that, I believe that your conditionals may not be executing as you expect. nextInt() will return a reasonable uniform random number in the range of -2147483648 to 2147483647. You have a 1/2^64 chance of getting a 0. Reduce the random number range to something more reasonable. For example, nextInt(10) will return a random number between 0 and 9.
Furthermore, if the probability is too low, you will not get 5 reds all the time. To guarantee 5 picks and for the sake of computational efficiency, it is better to randomly pick array indices and evaluate whether a color is set or not, such as the following pseudo-code
int redTot = 0;
while ( redTot < 5 ) {
int r = rn.nextInt( 5 );
int c = rn.nextInt( 5 );
String color = fullmap.get( r ).get( c );
if ( color == null ) {
fullmap.get( r ).set( c, "Red" );
redTot++;
}
}

Is there an Iterator-like function (or workaround) for Arrays?

I am trying to add a sequence of letters as Strings to a 2D array. So object [17] goes to endState[0][0]; [18] to endState[0][1] and so forth.
The problem I have is with the outside for loop, which just adds object at [32] to all of the cells in the matrix. Normally I would use an iterator to deal with this when using other collections, however, it is not possible with arrays as far as i am aware (I am a novice as you may have guessed).
String [][] endState = new String[4][4];
for(int i1=17;i1<33;i1++){
for(int r=0;r<endState.length;r++){
for(int c=0;c<endState.length;c++){
endState[r][c] = config.split("")[i1];
}
}
}
Any suggestions on how I can overcome this?
Many thanks.

Do you need something like that ?
String[] configs = config.split("");
String [][] endState = new String[4][4];
int i = 17;
for(int r=0;r<endState.length;r++){
for(int c=0;c<endState.length;c++){
endState[r][c] = configs[i++];
}
}

If you want to turn the letters into a gird you can do.
String[] letters = config.substring(17).split("");
String[][] endState = new String[4][];
for (int i = 0; i < endState.length; i++)
endState[i] = Arrays.copyOf(letters, i * 4, 4);
or you could do
String[][] endState = IntStream.range(0, 4)
.mapToObject(i -> Arrays.copyOf(letters, i * 4, 4))
.toArray(s -> new String[s][]);

If you use Java 8, you can do it as follows:
Arrays.asList(someArray).foreach(item -> {});
or
Arrays.asList(someArray).stream().ANY_STREAM_FUNCTION_HERE
If you want iterate your 2dim array:
Arrays.asList(someArray).foreach(item -> {
Arrays.asList(item).foreach(item2 -> {[Do your job here]})
});
You can do it more Java 7 way:
for(item : Arrays.asList(someArray)) {
...
}
Anyway you can always use Arrays.asList(someArray) to obtain a list from array.

Java Array Creation and Array Name Change

Can you create a line of code, within a while-loop, that will create a new array AND change the array's name with each iteration of the while loop?
Example:
int size = 10;
int name_count = 1;
while(size <= 100)
{
//name_count is changing the name of the array by calling it
// "array1", "array2", etc...
//I know this may not be correct code for changing the name of
// the array, but it is suppose to get the point across.
int[] array(name_count) = new int[size];
for (int i = 0; i <= size; i++)
{ /* Adding numbers to an array */ }
size = size + 5;
name_count++;
}

Identifier names need to be defined at compile time. So you can't explicitly use a different variable name on each iteration of the loop.
Another problem with your pseudo-code is that, if the array were to be declared inside the loop, it would fall out of scope when the loop completes, so there wouldn't be much point.
To do something like this you need to use some collection to hold the arrays, and it would be easier to make them explicit objects instead of just arrays. Something like:
List<List<Integer>> listOfArrays = new ArrayList<List<Integer>>();
while (size <= 100) {
List<Integer> listOfNumbers = new ArrayList<Integer>(size);
/* insert loop here to add numbers to listOfNumber */
size += 5;
name_count += 1;
}
Then you can access each list of numbers using an index into listOfArrays -- equivalent to naming each one with the index, but handled at runtime instead of compile time.

You cannot change the array's name, It will just re-declare the array with each successful loop. (It will be a new blank array.) I think what you are looking for is a two dimensional array.
int[][] myArray = new int[3][3];

Can I declare and initialize an array with the same instruction in Java?

Is there a way to do the following at the same time?
static final int UN = 0; // uninitialized nodes
int[] arr;
// ... code ...
arr = new int[size];
for (int i = 0; i < 5; i++) {
arr[i] = UN;
}
Basically, I want to declare arr once I know what its size will be and initialize it to UN without having to loop. So something like this:
int[] arr = new int[size] = UN;
Is this possible?
Thanks.

Arrays.fill(arr, UN);

You don't need to initialize them with 0. An int defaults to 0 already.
Just
int[] array = new int[size];
is enough. It gives you an array of zeroes of the given length. If it were an Integer[], it would have been an array of nulls.

Well, in the case of objects (or primitives with autoboxing) you can do the following:
int count = 20;
final int UN = 0;
Integer[] values = Collections.nCopies(count, UN).toArray(new Integer[count]);
The downsides are that you have to use the object forms of the primitives (since the Collections must be of objects) and a separate List will be constructed and then thrown away. This would allow you to create the array as one statement however.

No, not with the standard libraries. If you write your own functions, though, you can easily do so in a single statement (not instruction; those are different). Mine looks like String[][] strings = Arrayu.fill(new String[x][y], "");
Here's a link. There's some junk in there too, though; I just posted a copy of the current source directly without cleaning it up.

No.
Next question?

int arr[] = { 0, 0, 0, 0, 0 };

Oops, read your question better:
You can init an array like so
int[] arr = new int[] {UN, UN, UN, UN, UN};
But ofcourse, if you don't know the size at compile time, then you have to do the for loop. The second technique is not possible.