Copying the first half of an ArrayList

Question

There is an ArrayList al, and I want to copy the first half of its elements into another ArrayList firstHalf. (If al

Answer 1

List<Integer> firstHalf = al.subList(0, (int) al.size() / 2 + 1);

Is easier convert the al.size() / 2 to integer than doing "%2".

You add 1 to firstHalf to be bigger than the second half.

Answer 2

You should use add instead of set:

int x = al.size()/2 + (al.size()%2) - 1;
for(int i = 0; i < x; i++){
    firstHalf.add(al.get(i));
 }

It would be better to use List#subList

Answer 3

List#subList is exactly suited for this purpose.

int chunkSize = al.size() % 2 == 0 ? al.size() / 2 : (al.size() / 2) + 1;
List<Integer> firstHalf = al.subList(0, chunkSize);

There are two cases to consider:

• Even: If the size is even, then n / 2 is the correct size to chunk by.
• Odd: If the size is odd, then you need to add 1 to the result for the odd-length list to have the middle value.

Answer 4

Another approach:

List<Integer> firstHalf = al.subList(0, al.size()/2 + (al.size()%2) - 1);