How to create 2D ArrayList and add elements

Question

I have a small program that hold pairs of states and their capitals in 2D array. Below this program:

public class StateCapitals {

public static void main(String[] args) {
    String[][] answers = {
            {"Alabama", "Montgomery"},
            {"Alaska", "Juneau"},
            {"Arizona", "Phoenix"},
            {"Arkansas", "Little Rock"},
            {"California", "Sacramento"},
            {"Colorado", "Denver"},
            {"Connecticut", "Hartford"},
            {"Delaware", "Dover"},
            {"Florida", "Tallahassee"},
            {"Georgia", "Atlanta"}
    };


    int correctCount = 0;

    for (int i = 0; i < answers.length; i++) {


        System.out.print("What is the capital of " + answers[i][0]);

        Scanner input = new Scanner(System.in);

        String userInput = input.nextLine();



        for (int j = 0; j < answers[i].length - 1; j++) {
            System.out.println("The correct answer should be " + answers[i][j + 1]);

            if(userInput.equals(answers[i][j + 1]))
                correctCount++;

        }


    }

    System.out.println("The correct count is " + correctCount);
    }
}

I need to replace regular 2D array with List<List<String>> super2dArray = new ArrayList<ArrayList<String>>().

I found some threads on stackoverflow how to add array that I want. Here is links: How to create an 2D ArrayList in java? andHow do I declare a 2D String arraylist?. But these discussions didn't explain how to add elements in each ArrayList. The best that I can do to create new ArrayList then add some elements and finally attached ArrayList to another one. They didn't explain how to add elements to 2D ArrayList.

Have you considered making a Country class with fields Name and Capital City? — George Simms, Feb 15 '15 at 21:48

score 0 · Accepted Answer · answered Feb 15 '15 at 21:44

0

Here a way easier example :)

Notice that I give a fixed initial length to the constructor of the ArrayList as we already know the length of the array.

List<List<String>> myListOfListOfString = new ArrayList<List<String>>(answers.length);

for(String[] array : answers)
    myListOfListOfString.add(Arrays.asList(array));

See documentation for more details.

answered Feb 15 '15 at 21:44

Jean-François Savard

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Thank you very much. That works. I have a question. If I don't know 2D array length and I have to add element dinamically how can I add elements to each ArrayList? – rob111 Feb 15 '15 at 21:58
@rob111 you can do it the same way, List will auto increment it length. – Jean-François Savard Feb 15 '15 at 21:58
Thank you very much. If I need to create N dimensional ArrayList I have to do enclosed for loops for adding elements. Is it right? – rob111 Feb 15 '15 at 22:19
@rob111 Arrays.asList does not matter of the length. – Jean-François Savard Feb 15 '15 at 22:37

How to create 2D ArrayList and add elements

1 Answers1