Separating array in other arrays

Question

I have an array that I need to split in different arrays. I have an array of Strings and need to split it in different pages (different arrays).

At first, I get the length of the array, using

int size = array.length;

And then, I get the number of pages I need, knowing that each page should only have 10 Strings

int numberOfPages = (int) Math.floor(size/10);

The user then select which page he wants to see

int pageSelected = 2;

After that, I tried to split the array, but got some exceptions. I tried:

Arrays.copyOfRange(array,(0+10*(pageSelected-1),10*10+(pageSelected-1)));

I get an exception when I try to print the values of the new array.

Is there anyway to split an array in 'pages', and display these 'pages' as requestes?

@Edit1 I get a Nullpointer Exception

Answer 1

The error probably occurs in this line:

Arrays.copyOfRange(array,(0+10*(pageSelected-1),10*10+(pageSelected-1)));

Where there is an error with the brackets (the method requires three arguments, but from the method's perspective, you only provide two: the last two are grouped by brackets). You can use:

Arrays.copyOfRange(array,10*(pageSelected-1),10*10+(pageSelected-1));

(removed 0+ since this has no use).

Furthermore you made a semantical error: 10*10+(pageSelected-1) should be replaced by: 10+10*(pageSelected-1

So the full line reads:

Arrays.copyOfRange(array,10*(pageSelected-1),10+10*(pageSelected-1));

Although a better guideline would be to use small steps:

int i = pageSelected-1;
int g = 10*i;
Arrays.copyOfRange(array,g,g+10);//do something with the result

And to do it perfect, you better use variables for constants such that - if you change your mind - you can easily modify the number of items per page:

int i = pageSelected-1;
int perpage = 10;
int g = perpage*i;
Arrays.copyOfRange(array,g,g+perpage);//do something with the result

Finally a small remark: as @j_v_wow_d says, you should ceil the division, otherwise you will generate one page for 11 items. The correct code for numberOfPages is thus:

int numberOfPages = (int) Math.ceil((double) size/perpage);

Answer 2

If the pageSelected is indexed so that 0 is the first:

String[] array = {"a", "b", "c", "d", "e", "f"};
int pageSize = 2;
int pageSelected = 2;
final String[] pageData =
        Arrays.copyOfRange(
                array,
                (pageSelected * pageSize),
                (pageSelected * pageSize) + pageSize);

The outcome of this is that pageData contains ["e", "f"].