Java 2d Array or 2d ArrayList?

Question

I am tasked with making a program that interfaces with a multivalue database. I receive the entire record in a string with delimeters for the values and subvalues. From there I split the data into a 2d array. Here's a snippet of one (notice the varying lengths):

        0           1           2
   +------------------------------------+
0  | 442        |           |           |
1  | C          |           |           |
2  |            |           |           |
3  | N          |           |           |
4  | LAND       |           |           |
5  | 05412300   | 05412307  |           |
6  | BEARING    |           |           |
7  | BRAND1     | BRAND2    | BRAND3    |
8  | 12         |           |           |
   +------------------------------------+

Now I've always used ArrayLists instead of Arrays because I knew it was best practice. Now I'm wondering if using a 2d ArrayList would be beneficial as well. I've looked at some examples and I don't quite understand how to get the values when I need them. If I were to do:

String[][] cheese = {
    {"chedder", "swiss", "pepperjack"},
    {"sliced", "cubed", "block"}
};
String myFavorite = cheese[0][2];

myFavorite would be pepperjack, but how would I do that with a 2d ArrayList? The example's I've found haven't been too helpful for me. I do know the exact number of rows (but not columns) of data I'll be receiving and the row number will not change so maybe a regular 2d array would be best practice?

Answer 1

Your data doesn't look like it belongs in a 2d array or list. If it were me I would create data structures that make sense for the data. If you must use a list of lists:

List<List<String>> cheese = new ArrayList<List<String>>();
cheese.add(Arrays.asList("cheddar", "swiss", "pepperjack"));
cheese.add(Arrays.asList("sliced", "cubed", "block"));

String myFavorite = cheese.get(0).get(2);

Answer 2

You can make a 2D ArrayList by making the members of your outer ArrayList themselves ArrayList s.

List<List<String>> cheese = new ArrayList<List<String>>();

Then you can add ArrayList<String> s to cheese .

favorites.add(new ArrayList<String>(Arrays.asList("cheddar", "swiss", "pepperjack")));
favorites.add(new ArrayList<String>(Arrays.asList("sliced", "cubed", "block")));

You can extract the elements with two successive get calls.

String myFavorite = cheese.get(0).get(2);

Answer 3

You can use the get function just like a single dimensional ArrayList. So, if your ArrayList is cheese, that has additional ArrayLists you can try something like this:

String myFavorite = cheese.get(0).get(2);

The first get will return the first ArrayList, and the second get will return the third item (second index) of said first ArrayList.

Answer 4

我没有示例，但是您应该能够制作一个ArrayLists的ArrayList并执行以下操作：

String myFavorite = cheese.get(0).get(2);