如何转换ArrayList <ArrayList<Integer> &gt;转换为int [] []？

Question

我有一个旧函数，我无法更改谁想要参数int [] []是否可以将ArrayList<ArrayList<Integer>>映射到int[][]

Answer 1

Get the size of the ArrayLists into i and j ,respectively Increment i and j according to your logic

int i = 0;
for(ArrayList<Integer> a1 : outer){
    int j=0;
    for(Integer k : a1){
       yourarray[i][j++] = k;
    }
    i++;
}

Answer 2

I agree with Maurice.

To convert List<Integer> to int[] , there's a nice answer here that you may find usefull.

Also note that Apache Commons has a ArrayUtils class , which has a method toPrimitive() that does exactly this for one array level.

Edit (see comments below):

msandiford also mentions the existence of guava Ints class that provides a static int[] toArray(Collection<Integer> collection) method.

Answer 3

我想您将需要两个级别的循环来做到这一点。