有没有办法将输入矩阵转换为 ArrayLists 的 ArrayList？

Question

Here is an example input that I want to make an ArrayList of ArrayLists:

1,0,1
1,1,1
0,0,1

I have Scanner in that holds the input and I was thinking of having a for-loop to add the numbers to the ArrayList of ArrayLists using in.nextInt() . But the problem is how do I find when I should move on to the next ArrayList within the big ArrayList?

Answer 1

You could either define an arbitrary limit of numbers before moving to the next ArrayList

while (condition to keep reading)
{
 for (int i = 0; i < arbitrarylimit; i++) {
   List<Integer> list = new ArrayList<Integer>();
   // read the input 
   biglist.add(list);
 }
}

Or you could establish that if you find a new line before a number then it should be inserted into a new ArrayList.

while (condition to keep reading)
{
   List<Integer> list = new ArrayList<Integer>();
   String result = scanner.nextLine();
   // split result and add it to a list
   biglist.add(list);
}

Answer 2

You can do it like this.

• read in each row as a single line
• Each number can be separated by commas and or spaces
• Use a stream and split them on the commas and spaces
  converting them to a List<Integer>
• Then add that list to the overall list of lists.

String line = "";
List<List<Integer>> lists = new ArrayList<>();
// take input until a `#` is typed on a new line.
while (sc.hasNextLine()) {
    List<Integer> nums = Arrays.stream(line.split("[\\s,]+"))
            .map(Integer::parseInt)
            .collect(Collectors.toList());
    lists.add(nums);
}
lists.forEach(System.out::println);

For the following input per line

1 0,1
1,1,1
0 0 1

You get the following output

[1, 0, 1]
[1, 1, 1]
[0, 0, 1]